研究者詳細 - 市岡　優典

論文 - 市岡　優典

分割表示 >> ／全件表示 188 件中 1 - 188 件目

Fractional Vortex Array Realized at Twin Boundary in a Nematic Superconductor 査読

Sakiko Noda, Hiroto Adachi, Masanori Ichioka

Journal of the Physical Society of Japan 2025年2月

Time-dependent Ginzburg-Landau theory of the vortex spin Hall effect 査読

Hiroto Adachi, Yusuke Kato, Jun-ichiro Ohe, Masanori Ichioka

Physical Review B 2024年5月

Supercurrent distribution in real-space and anomalous paramagnetic response in a superconducting quasicrystal 査読

Takumi Fukushima, Nayuta Takemori, Shiro Sakai, Masanori Ichioka, Anuradha Jagannathan

Physical Review Research 2023年11月

Supercurrent Distribution on Ammann-Beenker Structure 査読

Takumi Fukushima, Nayuta Takemori, Shiro Sakai, Masanori Ichioka, Anuradha Jagannathan

Journal of Physics: Conference Series 2461 ( 1 ) 2023年

掲載種別：研究論文（国際会議プロシーディングス）

We study the distribution of supercurrent in the attractive Hubbard model on a periodic approximant of the Ammann-Beenker structure by means of the Bogoliubov-de Gennes (BdG) mean-field theory. We first investigate the spatial distributions of the electron density and superconducting order parameter and find a crossover between superconducting states with (i) extended, (ii) localized, and (iii) short-ranged Cooper pairs, similar to the previous results on the Penrose tiling. Furthermore, we formulate the expression of the supercurrent for the periodic approximant in terms of the eigenenergies and the wave functions of the Bogoliubov-de Gennes Hamiltonian and numerically investigate how the local supercurrent distribution varies by changing the direction of the applied phase gradient.

DOI： 10.1088/1742-6596/2461/1/012014

Evidence for a Square-Square Vortex Lattice Transition in a High- Tc Cuprate Superconductor 査読

D. J. Campbell, M. Frachet, S. Benhabib, I. Gilmutdinov, C. Proust, T. Kurosawa, N. Momono, M. Oda, M. Horio, K. Kramer, J. Chang, M. Ichioka, D. Leboeuf

Physical Review Letters 129 ( 6 ) 2022年8月

掲載種別：研究論文（学術雑誌）

Using sound velocity and attenuation measurements in high magnetic fields, we identify a new transition in the vortex lattice state of La2-xSrxCuO4. The transition, observed in magnetic fields exceeding 35 T and temperatures far below zero field Tc, is detected in the compression modulus of the vortex lattice, at a doping level of x=p=0.17. Our theoretical analysis based on Eilenberger's theory of the vortex lattice shows that the transition corresponds to the long-sought 45° rotation of the square vortex lattice, predicted to occur in d-wave superconductors near a van Hove singularity.

DOI： 10.1103/PhysRevLett.129.067001

Antiferromagnetic spin Seebeck effect across the spin-flop transition: A stochastic Ginzburg-Landau simulation

Yutaka Yamamoto, Masanori Ichioka, Hiroto Adachi

Physical Review B 105 ( 10 ) 2022年3月

Spin Hall effect generated by fluctuating vortices in type-II superconductors 査読

Takuya Taira, Yusuke Kato, Masanori Ichioka, Hiroto Adachi

PHYSICAL REVIEW B 103 ( 13 ) 2021年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We theoretically investigate the vortex spin Hall effect, i.e., a novel spin Hall effect driven by the motion of superconducting vortices, by focusing on the role of superconducting fluctuations. Within the BCS-Gor'kov microscopic approach combined with the Kubo formula, we find a strong similarity between the vortex spin Hall effect and the vortex Nernst/Ettingshausen effect. Calculated temperature dependence of the voltage signal due to the inverse vortex spin Hall effect exhibits a strong enhancement by vortex fluctuations. This result not only provides a possible explanation for a prominent peak found in the spin Seebeck effect in a NbN/Y3Fe5O12 system but also leads to a proposal of new experiments using other superconductors with strong fluctuations, such as cuprate or iron-based superconductors.

DOI： 10.1103/PhysRevB.103.134417

Nonmagnetic impurity effect in vortex states of chiral superconductors 査読

Takahiro Ueda, Yasuaki Sera, Hiroto Adachi, Masanori Ichioka

PHYSICAL REVIEW B 103 ( 1 ) 2021年1月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Nonmagnetic impurity scattering effects in the vortex states are studied in the Born and the unitary limits for chiral superconductors by Eilenberger theory. We compare the spatial structure of the pair potential and local electronic structure in chiral p-wave superconductors with those in two types of chiral d-wave superconductors; d(1 +/-) d(xz) +/- id(yz) and d(2 +/-) d(x2-y2 )+/- id(xy) pairing Similar behaviors of the pair potentials are seen in p +/- - and d(1 +/-) -wave superconductors. In chiral d-wave superconductors, due to lack of Majorana properties relating to the s-wave Cooper pair amplitude, zero-energy vortex bound states are easily destroyed by the impurity scattering, compared to the Born limit in the chiral p_-wave superconductors. This decay is also seen in the unitary limit in the chiral p_ -wave superconductors. These differences are also discussed in the relation to s-wave Cooper pair amplitude and the local scattering rate. The impurity effects are also compared with those in s-wave superconductors.

DOI： 10.1103/PhysRevB.103.014506

Vortex Cores in Narrow Thin-Film Strips 査読

Vladimir G. Kogan, Masanori Ichioka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 89 ( 9 ) 2020年9月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We study vortex current distributions in narrow thin-film superconducting strips with the help of analytic expression of the vortex current derived within the London theory. Using definition of the vortex core "boundary" as a curve where the current reaches the depairing value, vortex core size and shape are estimated as a function of vortex position in the strip. We show that the core size near the strip edges is smaller than in the rest of the strip, indicating that the BardeenStephen flux-flow resistivity should be reduced near the edges. Moreover, at elevated temperatures, when the depairing current is small, the vortex core may extend to the whole strip width, thus turning into an edge-to-edge phase-slip line.

DOI： 10.7566/JPSJ.89.094711

Microscopic Eilenberger theory of Fulde-Ferrell-Larkin-Ovchinnikov states in the presence of vortices 査読

Kenta M. Suzuki, Kazushige Machida, Yasumasa Tsutsumi, Masanori Ichioka

PHYSICAL REVIEW B 101 ( 21 ) 2020年6月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We theoretically investigate the Fulde-Ferrell-Larkin-Ovchinnikov state by using the microscopic quasiclassical Eilenberger equation. The Pauli paramagnetic effects and the orbital depairing effects due to vortices are treated on an equal footing for three-dimensional spherical Fermi surface model and s-wave pairing. The field evolution of the Larkin-Ovchinnikov (LO) state is studied in detail, such as the H-T phase diagram, spatial structures of the order parameter, the paramagnetic moment, and the internal field. Field dependences of various thermodynamic quantities-the paramagnetic moment, entropy, and the zero-energy density of states-are calculated. Those quantities are shown to start quickly growing upon entering the LO state. We also evaluate the wavelength of the LO modulation, the flux line lattice form factors for small-angle neutron scattering, and the NMR spectra to facilitate the identification of the LO state. Two cases of strong and intermediate Pauli paramagnetic effect are studied comparatively. The possibility of the LO phase in Sr2RuO4, CeCoIn5, CeCu2Si2, and the organic superconductors is critically examined and crucial experiments to identify it are proposed.

DOI： 10.1103/PhysRevB.101.214516

Spin pumping into a spin glass material 査読

Yusei Fujimoto, Masanori Ichioka, Hiroto Adachi

PHYSICAL REVIEW B 101 ( 18 ) 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Spin pumping is a recently established means for generating a pure spin current, whereby spins are pumped from a magnet into the adjacent target material under the ferromagnetic resonance condition. We theoretically investigate the spin pumping from an insulating ferromagnet into spin glass materials. Combining a dynamic theory of spin glasses with the linear-response formulation of the spin pumping, we calculate temperature dependence of the spin pumping near the spin glass transition. The analysis predicts that a characteristic peak appears in the spin pumping signal, reflecting that the spin fluctuations slow down upon the onset of spin freezing.

DOI： 10.1103/PhysRevB.101.184412

Variation of zero-energy density of states of a d-wave superconductor in a rotating in-plane magnetic field: Effect of nonmagnetic impurities 査読

Yuuki Hashitani, Kenta K. Tanaka, Hiroto Adachi, Masanori Ichioka

PHYSICAL REVIEW B 101 ( 6 ) 2020年2月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Oscillation of zero-energy density of states under the rotation of an in-plane magnetic field is used to identify node positions of the superconducting gap. Based on Eilenberger theory that can capture the vortex core contribution appropriately, we quantitatively study the effects of nonmagnetic impurity scattering on the oscillation in a d(x2-y2) -wave superconductor, as a function of the magnetic field and the scattering rate in the Born and the unitary limits. We find that the sign of the oscillation can be changed by the impurity scattering at low fields, indicating that impurity effect is an important factor in the analysis of angle-resolved specific heat measurements.

DOI： 10.1103/PhysRevB.101.060501

Relation of Superconducting Pairing Symmetry and Non-Magnetic Impurity Effects in Vortex States 査読

Yasuaki Sera, Takahiro Ueda, Hiroto Adachi, Masanori Ichioka

SYMMETRY-BASEL 12 ( 1 ) 2020年1月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MDPI

Non-magnetic impurity scattering effects on the vortex core states are theoretically studied to clarify the contributions from the sign-change of the pairing function in anisotropic superconductors. The vortex states are calculated by the Eilenberger theory in superconductors with px-wave pairing symmetry, as well as the corresponding anisotropic s-wave symmetry. From the spatial structure of the pair potential and the local electronic states around a vortex, we examine the differences between anisotropic superconductors with and without sign-change of the pairing function, and estimate how twofold symmetric vortex core images change with increasing the impurity scattering rate both in the Born and the unitary limits. We found that twofold symmetric vortex core image of zero-energy local density of states changes the orientation of the twofold symmetry with increasing the scattering rate when the sign change occurs in the pairing function. Without the sign change, the vortex core shape reduces to circular one with approaching dirty cases. These results of the impurity effects are valuable for identifying the pairing symmetry by observation of the vortex core image by the STM observation.

DOI： 10.3390/sym12010175

Spin Seebeck effect in paramagnets and antiferromagnets at elevated temperatures 査読

Yutaka Yamamoto, Masanori Ichioka, Hiroto Adachi

PHYSICAL REVIEW B 100 ( 6 ) 2019年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We develop a theory of the spin Seebeck effect (SSE) in paramagnets as well as in antiferromagnets at elevated temperatures where the classical limit of the fluctuation-dissipation theorem is applicable. Employing dissipative stochastic models that are valid at these temperatures, we calculate the SSE signal, and we find that both the paramagnetic SSE and the antiferromagnetic SSE are expressed by a single equation that is proportional to the external magnetic field times the spin susceptibility of the magnet. The present result suggests the appearance of a cusp structure at the Neel temperature in the antiferromagnetic SSE signal.

DOI： 10.1103/PhysRevB.100.064419

Paramagnetic Pair-Breaking in Spin-Triplet Superconductors with Spin-Orbit Coupling: Application to Sr2RuO4 査読

Koushi Oda, Kenta K. Tanaka, Seiichiro Onari, Masanori Ichioka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 88 ( 6 ) 2019年6月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Paramagnetic pair-breaking effects by in-plane magnetic fields are studied in the presence of the spin-orbit coupling, based on the tight-binding three-orbital model for Sr2RuO4. The spin-orbit coupling interfere with the paramagnetic pair-breaking effects in the spin-singlet pairing and the spin-triplet helical p-wave superconductors. We show how the superconducting transition temperature T-c depends on the field orientation and the pairing symmetry. In the spin-triplet chiral p-wave superconductors, as the condition for that the paramagnetic pair-breaking works even to the in-plane fields, we need the mixing of different d-orbital electrons by the c-direction hopping, in addition to the spin-orbit coupling. We also study a case of the change from the helical to chiral p-wave states by the paramagnetic effect.

DOI： 10.7566/JPSJ.88.064707

Spin diffusion equation in superconductors in the vicinity of T-c 査読

Takuya Taira, Masanori Ichioka, So Takei, Hiroto Adachi

PHYSICAL REVIEW B 98 ( 21 ) 2018年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We microscopically derive the spin diffusion equation in an s-wave superconductor in the vicinity of the superconducting transition temperature T-c. Applying the general relation between the relaxation function and the response function to the present spin diffusion problem, we examine how the spin relaxation time and the spin diffusion coefficient are renormalized in the superconducting state. The analysis reveals that, below T-c, both the spin relaxation time and the spin diffusion coefficient are increased, resulting in an enhancement of the spin diffusion length. The present result may provide an explanation for the recent observation of an enhanced spin pumping signal below T-c in a Py/Nb/Pt system that is free from the coherence peak effect.

DOI： 10.1103/PhysRevB.98.214437

Theoretical analysis for spin-polarized local density of states in the vortex state of helical p-wave superconductors 査読

Kenta K Tanaka, Masanori Ichioka, Seiichiro Onari

Journal of Physics: Conference Series 969 ( 1 ) 2018年4月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Institute of Physics Publishing

Based on the quasi-classical Eilenberger theory, we calculate the site-dependence of order-parameter and spin-polarized local density of states (LDOS) in the vortex lattice state of helical p-wave superconductors. The spin-polarized LDOS is induced around the vortex core by the vorticity coupling to the chirality of up-spin pair or down-spin pair. In order to distinguish the d-vector symmetry, we investigate the magnetic eld effect on the spatial structure of the spin-polarized LDOS.

DOI： 10.1088/1742-6596/969/1/012043

Local NMR relaxation rates T1-1 and T2-1 depending on the d -vector symmetry in the vortex state of chiral and helical p -wave superconductors 査読

Kenta K. Tanaka, Masanori Ichioka, Seiichiro Onari

Physical Review B 97 ( 13 ) 2018年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Physical Society

Local NMR relaxation rates in the vortex state of chiral and helical p-wave superconductors are investigated by the quasiclassical Eilenberger theory. We calculate the spatial and resonance frequency dependences of the local NMR spin-lattice relaxation rate T1-1 and spin-spin relaxation rate T2-1. Depending on the relation between the NMR relaxation direction and the d-vector symmetry, the local T1-1 and T2-1 in the vortex core region show different behaviors. When the NMR relaxation direction is parallel to the d-vector component, the local NMR relaxation rate is anomalously suppressed by the negative coherence effect due to the spin dependence of the odd-frequency s-wave spin-triplet Cooper pairs. The difference between the local T1-1 and T2-1 in the site-selective NMR measurement is expected to be a method to examine the d-vector symmetry of candidate materials for spin-triplet superconductors.

DOI： 10.1103/PhysRevB.97.134507

Spin Seebeck effect in a simple ferromagnet near Tc: a Ginzburg-Landau approach 査読

Hiroto Adachi, Yutaka Yamamoto, Masanori Ichioka

Journal of Physics D: Applied Physics 51 ( 14 ) 144001(1) - 144001(1)-144001(5) 2018年

Pair breaking of multigap superconductivity under parallel magnetic fields in the electric-field-induced surface metallic state 査読

Masahiro Nabeta, Kenta K. Tanaka, Seiichiro Onari, Masanori Ichioka

PHYSICAL REVIEW B 96 ( 9 ) 296 - 303 2017年9月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The roles of paramagnetic and diamagnetic pair-breaking effects in superconductivity in the electric-fieldinduced surface metallic state are studied using the Bogoliubov-de Gennes equation when magnetic fields are applied parallel to the surface. The multigap states of the subbands are related to the depth dependence and the magnetic field dependence of the superconductivity. In the Fermi-energy density of states and the spin density, subband contributions successively appear from higher-level subbands with increasing magnetic fields. The characteristic magnetic field dependence may be a key feature to identify the multigap structure of the surface superconductivity.

DOI： 10.1103/PhysRevB.96.094522

Paramagnetic and diamagnetic pair-breaking effect in electric-field-induced surface superconductivity under parallel magnetic fields 査読

Masanori Ichioka, Masahiro Nabeta, Kenta K. Tanaka, Seiichiro Onari

Journal of Physics: Conference Series 871 ( 1 ) 47 - 55 2017年7月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Institute of Physics Publishing

Electric-field-induced surface superconductivity is studied by Bogoliubov-de Gennes equation under magnetic fields parallel to the surface. We estimate the pair-breaking effects by the paramagnetic Zeeman shift and by diamagnetic screening current. We find that the depth dependences of pair potential, screening current, spin current, and paramagnetic moment under the magnetic fields reflect the multi-gap superconductivity in the sub-band structure.

DOI： 10.1088/1742-6596/871/1/012001

Spin-polarized local density of states around vortex in helical p-wave superconductors 査読

Kenta K. Tanaka, Masanori Ichioka, Seiichiro Onari

Journal of Physics: Conference Series 871 ( 1 ) 249 - 252 2017年7月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Institute of Physics Publishing

Based on the quasi-classical Eilenberger theory, we investigate the magnetic field dependence of order-parameters and spin-polarized local density of states (LDOS) in the vortex lattice state of helical p-wave superconductors. The spin-polarized LDOS is induced by the vorticity coupling to the chirality of up-spin pair or down-spin pair, even when Knight shift does not change. We clarify the instability of the helical p-wave state at high field, and that the spin-polarized LDOS shows the unique behaviors of the helical p-wave state.

DOI： 10.1088/1742-6596/871/1/012024

Spin pumping into superconductors: A new probe of spin dynamics in a superconducting thin film 査読

Masashi Inoue, Masanori Ichioka, Hiroto Adachi

PHYSICAL REVIEW B 96 ( 2 ) 239 - 249 2017年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Spin pumping refers to the microwave-driven spin current injection from a ferromagnet into the adjacent target material. We theoretically investigate the spin pumping into superconductors by fully taking account of impurity spin-orbit scattering that is indispensable to describe diffusive spin transport with finite spin diffusion length. We calculate temperature dependence of the spin pumping signal and show that a pronounced coherence peak appears immediately below the superconducting transition temperature T-c, which survives even in the presence of the spin-orbit scattering. The phenomenon provides us with a new way of studying the dynamic spin susceptibility in a superconducting thin film. This is contrasted with the nuclear magnetic resonance technique used to study a bulk superconductor.

DOI： 10.1103/PhysRevB.96.024414

Spin-polarized local density of states in the vortex state of helical p-wave superconductors 査読

Kenta K. Tanaka, Masanori Ichioka, Seiichiro Onari

PHYSICAL REVIEW B 95 ( 13 ) 23 - 40 2017年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Properties of the vortex state in helical p-wave superconductor are studied by the quasiclassical Eilenberger theory. We confirm the instability of the helical p-wave state at high fields and that the spin-polarized local density of states M(E, r) appears even when Knight shift does not change. This is because the vorticity couples to the chirality of up-spin pair or down-spin pair of the helical state. In order to identify the helical p-wave state at low fields, we investigate the structure of the zero-energyM(E = 0, r) in the vortex states, and also the energy spectra of M(E, r).

DOI： 10.1103/PhysRevB.95.134502

Locking of length scales in two-band superconductors 査読

M. Ichioka, V. G. Kogan, J. Schmalian

PHYSICAL REVIEW B 95 ( 6 ) 1517 - 1523 2017年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

A model of a clean two-band s-wave superconductor with cylindrical Fermi surfaces, different Fermi velocities v(1),(2), and a general 2x2 coupling matrix V-alpha beta is used to study the order parameter distribution in vortex lattices. The Eilenberger weak coupling formalism is used to calculate numerically the spatial distributions of the pairing amplitudes Delta(1) and Delta(2) of the two bands for vortices parallel to the Fermi cylinders. For generic values of the interband coupling V-12, it is shown that, independently of the couplings V-alpha beta, of the ratio v(1)/v(2), of the temperature, and the applied field, the length scales of spatial variation of Delta(1) and of Delta(2) are the same within the accuracy of our calculations. The only exception from this single length-scale behavior is found for V-12 << V-11, i.e., for nearly decoupled bands.

DOI： 10.1103/PhysRevB.95.064512

Pair-breaking effects by parallel magnetic field in electric-field-induced surface superconductivity 査読

Masahiro Nabeta, Kenta K. Tanaka, Seiichiro Onari, Masanori Ichioka

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 530 8 - 10 2016年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We study paramagnetic pair-breaking in electric-field-induced surface superconductivity, when magnetic field is applied parallel to the surface. The calculation is performed by Bogoliubov-de Gennes theory with s-wave pairing, including the screening effect of electric fields by the induced carriers near the surface. Due to the Zeeman shift by applied fields, electronic states at higher-level sub-bands become normal-state-like. Therefore, the magnetic field dependence of Fermi-energy density of states reflects the multi-gap structure in the surface superconductivity. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2016.04.006

Effects of vorticity and impurity on NMR relaxation rate in chiral p-wave superconductors 査読

Kenta K. Tanaka, Masanori Ichioka, Seiichiro Onari

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 530 62 - 64 2016年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

In order to study site-selective NMR in chiral p -wave superconductors, we calculate local nuclear relaxation rate T-1(-1) in the vortex lattice state by Eilenberger theory with and without non-magnetic impurity scattering in the Born limit and unitary limit. The local T-1(-1) in the NMR resonance line shape is different between two chiral states p(+/-), depending on whether the chirality is parallel or anti-parallel to the vorticity. In the p(-)-wave, anomalous suppression of local T-1(-1) occurs around the vortex core due to the negative coherence term coming from odd-frequency s-wave Cooper pair induced around the vortex. We especially examine the site dependence of the anomalous suppression of local T-1(-1), including the applied magnetic field dependence and the impurity effects. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2016.03.003

Site-selective NMR for odd-frequency Cooper pairs around vortex in chiral p-wave superconductors 査読

Kenta K. Tanaka, Masanori Ichioka, Seiichiro Onari

PHYSICAL REVIEW B 93 ( 9 ) 094507-1-094507-5 2016年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

In order to identify the pairing symmetry with chirality, we study site-selective NMR in chiral p-wave superconductors. We calculate local nuclear relaxation rate T-1(-1) in the vortex lattice state by Eilenberger theory, including the applied magnetic field dependence. We find that T-1(-1) in the NMR resonance line shape is different between two chiral states p +/-(= p(x)+/- ip(y)), depending on whether the chirality is parallel or antiparallel to the vorticity. Anomalous suppression of T-1(-1) occurs around the vortex core in the chiral p(-) wave due to the negative coherence term coming from the odd-frequency s-wave Cooper pair induced around the vortex with Majorana state.

DOI： 10.1103/PhysRevB.93.094507

Symmetry-Protected Topological Superfluids and Superconductors-From the Basics to He-3 査読

Takeshi Mizushima, Yasumasa Tsutsumi, Takuto Kawakami, Masatoshi Sato, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 85 ( 2 ) 022001-1-022001-74 2016年3月

記述言語：英語出版者・発行元：PHYSICAL SOC JAPAN

In this article, we give a comprehensive review of recent progress in research on symmetry-protected topological superfluids and topological crystalline superconductors, and their physical consequences such as helical and chiral Majorana fermions. We start this review article with the minimal model that captures the essence of such topological materials. The central part of this article is devoted to the superfluid He-3, which serves as a rich repository of novel topological quantum phenomena originating from the intertwining of symmetries and topologies. In particular, it is emphasized that the quantum fluid confined to nanofabricated geometries possesses multiple superfluid phases composed of the symmetry-protected topological superfluid B-phase, the A-phase as a Weyl superfluid, the nodal planar and polar phases, and the crystalline ordered stripe phase. All these phases generate noteworthy topological phenomena, including topological phase transitions concomitant with spontaneous symmetry breaking, Majorana fermions, Weyl superfluidity, emergent supersymmetry, spontaneous edge mass and spin currents, topological Fermi arcs, and exotic quasiparticles bound to topological defects. In relation to the mass current carried by gapless edge states, we also briefly review a longstanding issue on the intrinsic angular momentum paradox in He-3-A. Moreover, we share the current status of our knowledge on the topological aspects of unconventional superconductors, such as the heavy-fermion superconductor UPt3 and superconducting doped topological insulators, in connection with the superfluid He-3.

DOI： 10.7566/JPSJ.85.022001

Transverse Components of Flux Line Lattice Form Factors in Uniaxial Superconductors 査読

Masanori Ichioka, Yuujirou Amano, Masahiro Ishihara, Kazushige Machida

PROCEEDINGS OF THE 28TH INTERNATIONAL SYMPOSIUM ON SUPERCONDUCTIVITY (ISS 2015) 81 77 - 80 2016年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：ELSEVIER SCIENCE BV

Magnetic field orientation dependence of transverse and longitudinal flux line lattice form factors are theoretically studied in uniaxial superconductors with extremely large anisotropy ratio 60 for some field magnitudes. The form factors are estimated by two methods, the Eilenberger theory and the London theory comparatively. We also compare them to the form factors observed by the small angle neutron scattering experiment on Sr2RuO4. We discuss the cutoff function of extended London theory, and the contributions from the suppression of the pair potential as a function of the field orientation. (C) 2016 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.phpro.2016.04.031

Hidden crossover phenomena in strongly Pauli-limited multiband superconductors: Application to CeCu2Si2 査読

Yasumasa Tsutsumi, Kazushige Machida, Masanori Ichioka

Physical Review B - Condensed Matter and Materials Physics 92 ( 2 ) 2015年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Physical Society

Motivated by recent experiments on heavy fermion materials CeCu2Si2 and UBe13, we develop a framework to capture generic properties of multiband superconductors with strong Pauli paramagnetic effect (PPE). In contrast to the single band case, the upper critical field Hc2 can remain a second-order transition even for strong PPE cases. The expected first-order transition is hidden inside Hc2 and becomes a crossover due to the interplay of multibandness. The present theory based on full self-consistent solutions of the microscopic Eilenberger theory explains several mysterious anomalies associated with the crossover and the "empty" vortex core state which is observed by recent STM experiment on CeCu2Si2.

DOI： 10.1103/PhysRevB.92.020502

Pauli paramagnetic effects on mixed-state properties in a strongly anisotropic superconductor: Application to Sr2RuO4 査読

Yuujirou Amano, Masahiro Ishihara, Masanori Ichioka, Noriyuki Nakai, Kazushige Machida

PHYSICAL REVIEW B 91 ( 14 ) 2015年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We study theoretically the mixed-state properties of a strong uniaxially anisotropic type-II superconductor with the Pauli paramagnetic effect, focusing on their behaviors when the magnetic field orientation is tilted from the conduction layer ab plane. On the basis of Eilenberger theory, we quantitatively estimate significant contributions of the Pauli paramagnetic effects on a variety of physical observables, including transverse and longitudinal components of the flux-line lattice form factors, magnetization curves, Sommerfeld coefficient, field distributions, and magnetic torques. We apply these studies to Sr2RuO4 and quantitatively explain several seemingly curious behaviors, including the H-c2 suppression for the ab-plane direction, the larger anisotropy ratio and intensity found by the spin-flip small-angle neutron scattering, and the first-order transition observed recently in magnetocaloric, specific-heat, and magnetization measurements in a coherent and consistent manner. Those lead us to conclude that Sr2RuO4 is either a spin-singlet or a spin-triplet pairing with the d-vector components in the ab plane.

DOI： 10.1103/PhysRevB.91.144513

Eilenberger theory for nuclear magnetic relaxation rate in superconducting vortex lattice state 査読

Kenta K. Tanaka, Masanori Ichioka, Seiichiro Onari, Noriyuki Nakai, Kazushige Machida

Physical Review B - Condensed Matter and Materials Physics 91 ( 1 ) 2015年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Physical Society

On the basis of the Eilenberger theory, spatial variation of the local NMR relaxation rate T1-1 is quantitatively estimated in the vortex lattice state, to clarify the differences between the s-wave and the d-wave superconductors. We study the temperature and the magnetic field dependencies of T1-1 inside and outside of the vortex core, including influences of nonmagnetic impurity scatterings in the Born limit and in the unitary limit. These results are helpful to detect detailed characters of local electronic structures in the vortex lattice states via site-selective NMR experiments.

DOI： 10.1103/PhysRevB.91.014509

Eilenberger and London theories for transverse components of flux line lattice form factors in uniaxial superconductors 査読

Yuujirou Amano, Masahiro Ishihara, Masanori Ichioka, Noriyuki Nakai, Kazushige Machida

PHYSICAL REVIEW B 90 ( 14 ) 2014年10月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We theoretically study the magnetic field orientation dependence of longitudinal and transverse flux line lattice form factors in uniaxial superconductors with anisotropy ratio corresponding to YBa2Cu3O7-delta. We discuss influences of the anisotropy ratio of coherence length and differences between the s-wave and the d(x2-y2)- wave pairings. The calculations are performed by two methods, the Eilenberger theory and the London theory comparatively, and we study the cutoff function of the extended London theory, which will be helpful in the analysis of the small angle neutron scattering in the vortex states.

DOI： 10.1103/PhysRevB.90.144514

Knight shift spectrum in vortex states in s- and d-wave superconductors on the basis of Eilenberger theory 査読

Kenta K. Tanaka, Masanori Ichioka, Noriyuki Nakai, Kazushige Machida

PHYSICAL REVIEW B 89 ( 17 ) 2014年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

From the spatial structure of vortex lattice state calculated by Eilenberger theory, we study the resonance line shape of Knight shift of the paramagnetic moments in s- and d-wave superconductors, comparing with the Redfield pattern of the internal field distribution. We discuss the deviation from the temperature dependence of the Yosida function and the magnetic field dependence of the paramagnetic susceptibility. In addition to the calculation in the clean limit, influences of the impurity scattering are estimated in the Born limit and in the unitary limit. These results are helpful for the analysis of NMR experiments to know properties of the superconductors.

DOI： 10.1103/PhysRevB.89.174504

Vortex States for Nearly B||ab in a Chiral p-Wave Superconductor (共著) 査読

M. Ichioka, M. Ishihara, Y. Amano, K. Machida

JPS Conference Proceedings 3 015014-1-015022-6 2014年

UPt3 as a Topological Crystalline Superconductor 査読

Yasumasa Tsutsumi, Masaki Ishikawa, Takuto Kawakami, Takeshi Mizushima, Masatoshi Sato, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 ( 11 ) 2013年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We investigate the topological aspect of the spin-triplet f-wave superconductor UPt3 through microscopic calculations of edge-and vortex-bound states based on the quasiclassical Eilenberger and Bogoliubov-de Gennes theories. It is shown that a gapless and linear dispersion exists at the edge of the ab-plane. This forms a Majorana valley, protected by the mirror chiral symmetry. We also demonstrate that, with increasing magnetic field, vortex-bound quasiparticles undergo a topological phase transition from topologically trivial states in the double-core vortex to zero-energy states in the normal-core vortex. As long as the d-vector is locked into the ab-plane, the mirror symmetry holds the Majorana property of the zero-energy states, and thus UPt3 preserves topological crystalline superconductivity that is robust against the crystal field and spin-orbit interaction.

DOI： 10.7566/JPSJ.82.113707

Influence on superconductivity in the parity mixing superconductor Li2T3B(T:Pt,Pd) by non-magnetic impurity and defect doping 査読

G. Bao, Y. Inada, G. Eguchi, Y. Maeno, M. Ichioka, G. -Q. Zheng

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 494 95 - 98 2013年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Superconductors with noncentrosymmetric crystal structures such as Li2T3B(T:Pd,Pt) have been the focus of in-depth research with their parity mixing nature. In this study, we focused our research on non-magnetic impurity effect in Li2T3B(T:Pd,Pt). The nature of the pair breaking by non-magnetic impurity in the parity mixing superconducting state is still unclear. We prepared different quality samples of Li2Pd3B and Li2Pt3B by changing conditions in synthesizing, and sample qualities were estimated by residual resistivity. Spin singlet dominant superconductor Li2Pd3B exhibits the weak T-c suppression attributed by nonmagnetic impurity and defects, while H-c2 (0) value increased. This behavior is similar in ordinary s-wave superconductor. On the other hand, for the spin triplet dominant superconductor Li2Pt3B, it was suggested that the Cooper pair was broken and superconducting gap was decreased by non-magnetic impurities and defects. Li2Pt3B is similar to unconventional superconducting state. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2013.04.059

Superconductivity in Ca-10(Ir4As8)(Fe2As2)(5) with Square-Planar Coordination of Iridium 査読

Kazutaka Kudo, Daisuke Mitsuoka, Masaya Takasuga, Yuki Sugiyama, Kento Sugawara, Naoyuki Katayama, Hiroshi Sawa, Hiroaki S. Kubo, Kenta Takamori, Masanori Ichioka, Tatsuo Fujii, Takashi Mizokawa, Minoru Nohara

SCIENTIFIC REPORTS 3 2013年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

We report the unprecedented square-planar coordination of iridium in the iron iridium arsenide Ca-10(Ir4As8)(Fe2As2)(5). This material experiences superconductivity at 16 K. X-ray photoemission spectroscopy and first-principles band calculation suggest Ir(II) oxidation state, which yields electrically conductive Ir4As8 layers. Such metallic spacer layers are thought to enhance the interlayer coupling of Fe2As2, in which superconductivity emerges, thus offering a way to control the superconducting transition temperature.

DOI： 10.1038/srep03101

Anisotropy of the Superconducting State in Sr2RuO4 査読

C. Rastovski, C. D. Dewhurst, W. J. Gannon, D. C. Peets, H. Takatsu, Y. Maeno, M. Ichioka, K. Machida, M. R. Eskildsen

PHYSICAL REVIEW LETTERS 111 ( 8 ) 2013年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Despite intense studies the exact nature of the order parameter in superconducting Sr2RuO4 remains unresolved. We have used small-angle neutron scattering to study the vortex lattice in Sr2RuO4 with the field applied close to the basal plane, taking advantage of the transverse magnetization. We measured the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane (similar to 60), which greatly exceeds the upper critical field anisotropy (similar to 20). Our result imposes significant constraints on possible models of triplet pairing in Sr2RuO4 and raises questions concerning the direction of the zero spin projection axis.

DOI： 10.1103/PhysRevLett.111.087003

領域6,領域8,領域11「超伝導位相制御:量子化・ダイナミクスの物理と応用展開」(第68回年次大会シンポジウムの報告,学会報告)

市岡優典

日本物理學會誌 68 ( 7 ) 478 - 478 2013年7月

Transverse magnetic field and chiral-nonchiral transition in vortex states for nearly B parallel to ab in chiral p-wave superconductors 査読

Masahiro Ishihara, Yuujirou Amano, Masanori Ichioka, Kazushige Machida

PHYSICAL REVIEW B 87 ( 22 ) 2013年6月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

On the basis of Eilenberger theory, we study the vortex state when a magnetic field is applied nearly parallel to the ab plane in a chiral p-wave superconductor with a large anisotropy ratio of ab and c, as in Sr2RuO4. We quantitatively estimate the field dependence of the pair potential, magnetization, and flux-line lattice form factor, and study the transition from the chiral p_ state at low fields to the nonchiral p(y) state at high fields. Even for exactly parallel fields to the ab plane, transverse fields exist in the chiral state. The chiral-nonchiral transition disappears when the magnetic field orientation is tilted within 1 degrees from the ab plane. This may be a reason why the experimental detection of this transition is difficult.

DOI： 10.1103/PhysRevB.87.224509

Rotation of Triangular Vortex Lattice in the Two-Band Superconductor MgB2 査読

Tomoya Hirano, Kenta Takamori, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 ( 6 ) 063708-1-063708-4 2013年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

To identify the contributions of the multiband nature and the anisotropy of a microscopic electronic structure to a macroscopic vortex lattice morphology, we develop a method based on the Eilenberger theory near Hc(2) combined with the first-principles band calculation to estimate the stable vortex lattice configuration. For a typical two-band superconductor MgB2, successive transitions of vortex lattice orientation that have been observed recently by small angle neutron scattering [Das et al.: Phys. Rev. Lett. 108 (2012) 167001] are explained by the characteristic fielddependence of two-band superconductivity and the competition of sixfold anisotropy between the sigma-and pi-bands. The reentrant transition at low temperature reflects the Fermi velocity anisotropy of the sigma-band.

DOI： 10.7566/JPSJ.82.063708

Surface Bound States and Spontaneous Current in Cyclic d-Wave Superconductors 査読

Masaki Ishikawa, Yasumasa Tsutsumi, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 ( 4 ) 2013年4月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

On the basis of Eilenberger theory, surface bound states and spontaneous current are studied in cyclic d-wave superconductors as a broken time-reversal symmetry of superconductivity in cubic lattice symmetry. We discuss how the spontaneous current and the electronic states depend on the orientation of the surface relative to the symmetry of superconductivity. The condition for topological Fermi arcs of zero-energy surface bound states to appear is identified in the complex pairing function of the cyclic d-wave.

DOI： 10.7566/JPSJ.82.043711

Multiple-gap structure in electric-field-induced surface superconductivity 査読

Yousuke Mizohata, Masanori Ichioka, Kazushige Machida

PHYSICAL REVIEW B 87 ( 1 ) 2013年1月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Local superconducting gap structure is studied as a function of nanoscale depth in electric-field-induced surface superconductivity such as in SrTiO3. We examine solutions of the Bogoliubov-de Gennes equation in two limiting confinement potential cases of an electric field with and without screening effects. As unique properties different from bulk superconductivity, there appear in-gap states even for isotropic s-wave pairing, due to the multiple-gap structure of sub-band-dependent surface superconductivity. These determine the depth dependence of local superconductivity. DOI: 10.1103/PhysRevB.87.014505

DOI： 10.1103/PhysRevB.87.014505

Field dependence of the specific heat in a heavy-fermion superconductor CeIrIn5 査読

Yuya Aoki, Shunichiro Kittaka, Toshiro Sakakibara, Akito Sakai, Satoru Nakatsuji, Yasumasa Tsutsumi, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 2012年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We investigated temperature, field, and field-orientation dependences of the specific heat of CeIrIn5. The upper critical field H-c2 was determined down to 80 mK from the specific heat measurements and exhibits a slight suppression at low temperatures. We revealed that the specific heat at 80 mK increases proportional to the square root of H up to nearly H-c2 for both H parallel to ab and H parallel to c, implying the presence of line nodes and a weak contribution of the Pauli paramagnetic pair-breaking effect. Furthermore, we revealed that the specific heat shows a fourfold oscillation under a rotating magnetic field in the ab plane. This result indicates that CeIrIn5 has fourfold symmetry around the c axis in its gap amplitude.

DOI： 10.1143/JPSJS.81SB.SB014

Odd-frequency Cooper-pair amplitude around a vortex core in a chiral p-wave superconductor in the quantum limit 査読

Takeshi Daino, Masanori Ichioka, Takeshi Mizushima, Yukio Tanaka

PHYSICAL REVIEW B 86 ( 6 ) 2012年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Solving the Bogoliubov-de Gennes equation, we study the spatial structure of odd-frequency s-wave Cooper-pair amplitudes at each quantized energy level of vortex bound states in chiral p-wave superconductors. For zero-energy Majorana states, the odd-frequency s-wave pair amplitude has the same spatial structure as that of the local density of states even in an atomic length scale. This relation also holds in finite energy bound states for single vortex winding antiparallel to the chirality, but not for parallel vortex winding. The double winding vortex case is also studied.

DOI： 10.1103/PhysRevB.86.064512

Superconducting gap structure of CeIrIn5 from field-angle-resolved measurements of its specific heat 査読

Shunichiro Kittaka, Yuya Aoki, Toshiro Sakakibara, Akito Sakai, Satoru Nakatsuji, Yasumasa Tsutsumi, Masanori Ichioka, Kazushige Machida

PHYSICAL REVIEW B 85 ( 6 ) 2012年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

In order to identify the gap structure of CeIrIn5, we measured field-angle-resolved specific heat C(phi) by conically rotating the magnetic field H around the c axis at low temperatures down to 80 mK. We revealed that C(phi) exhibits a fourfold angular oscillation, whose amplitude decreases monotonically by tilting H out of the ab plane. Detailed microscopic calculations based on the quasiclassical Eilenberger equation confirm that the observed features are uniquely explained by assuming the d(x2-y2)-wave gap. These results strongly indicate that CeIrIn5 is a d(x2-y2)-wave superconductor and suggest the universal pairing mechanism in CeMIn5 (M = Co, Rh, and Ir).

DOI： 10.1103/PhysRevB.85.060505

On Intrinsic Angular Momentum due to Edge Mass Current for Superfluid He-3 A-Phase 査読

Y. Tsutsumi, T. Mizushima, M. Ichioka, K. Machida

26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

In the superfluid He-3 A-phase, the edge mass current which accompanies surface Andreev bound states flows due to topological features. We discuss the relation between the angular momentum by the edge mass current and the macroscopic intrinsic angular momentum = N (h) over bar /2 by the Cooper pairs with aligned angular momenta, based on the quasi-classical theory. At the low temperature limit, half of the edge mass current from the bound state is canceled by that from the continuum state. Then, the magnitude of the total angular momentum is L = N (h) over bar /2 which corresponds to the macroscopic intrinsic angular momentum of N particles. The net angular momentum decreases monotonously toward zero at the transition temperature. However, that is larger than the macroscopic intrinsic angular momentum expected from the same behavior of the superfluid density in middle temperatures.

DOI： 10.1088/1742-6596/400/1/012076

Majorana Fermions Bound at Vortices and Surface of Superfluid He-3 査読

T. Mizushima, T. Kawakami, Y. Tsutsumi, M. Ichioka, K. Machida

26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We investigate the Majorana fermions bound at vortices and specular surface of superfluid He-3 A- and B-phases. It is demonstrated that the statistics of the integer vortex which is competitive to the half-quantum vortex is sensitive to the orientation of the magnetic field. We also discuss the surface Andreev bound state in the B-phase, which is expected to behave as Majorana fermions at the zero field limit. Based on the quasiclassical and Bogoliubov-de Gennes theories, we clarify that in the presence of the magnetic field parallel to the surface, the stable configuration of the (n) over cap -vector, which reflects the spin-orbit symmetry breaking, traces the point at which the surface state has the maximum gap.

DOI： 10.1088/1742-6596/400/1/012051

Vortex States of Chiral p-wave Superconductors 査読

M. Ichioka, K. Machida, J. A. Sauls

26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

In chiral p-wave superconductors a flux lattice of doubly quantized vortices is shown to be energetically stable for fields H-c1 < H-FL < H < H-c2, while at low fields a lattice of singly quantized vortices is stable. Here we report self-consistent calculations by Eilenberger theory for spatial structures of the pair potential and current density for vortex states of single- and double-winding vortices in chiral p-wave superconductors with a cylindrical Fermi surface.

DOI： 10.1088/1742-6596/400/2/022031

Field Evolution of the Fulde-Ferrell-Larkin-Ovchinnikov State in a Superconductor with Strong Pauli Effects 査読

Kenta M. Suzuki, Yasumasa Tsutsumi, Noriyuki Nakai, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( 12 ) 2011年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in the vortex lattice state is quantitatively studied using the self-consistent Eilenberger theory in three-dimensional (3D) space. We estimate free energy to determine the FFLO phase diagram in the H-T plane and stable FFLO wave number in the isotropic system with the 3D Fermi sphere and s-wave pairing. To facilitate the experimental identification of the FFLO state, we investigate the field evolution of NMR spectra and flux line lattice form factors obtained in neutron scattering in the FFLO vortex states. Possible applications of our results to experimental data on CeCoIn5 are mentioned.

DOI： 10.1143/JPSJ.80.123706

Origin of Spontaneous Broken Mirror Symmetry of Vortex Lattices in Nb 査読

Hiroki M. Adachi, Masaki Ishikawa, Tomoya Hirano, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( 11 ) 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Combining the microscopic Eilenberger theory with the first-principles band calculation, we investigate the stable flux line lattice (FLL) for a field applied to the fourfold axis, i.e., H parallel to [001] in cubic Nb. The observed FLL transformation along H-c2 is almost perfectly explained without using adjustable parameter, including the tilted square, scalene triangle with broken mirror symmetry, and isosceles triangle lattices upon increasing T. We construct a minimum Fermi surface model to understand such morphologies, particularly the stability of the scalene triangle lattice attributed to the lack of mirror symmetry about the Fermi velocity maximum direction in k-space.

DOI： 10.1143/JPSJ.80.113702

Multiple superconducting gap and anisotropic spin fluctuations in iron arsenides: Comparison with nickel analog 査読

Z. Li, S. Kawasaki, T. Oka, T. Tabuchi, Y. Ooe, M. Ichioka, Z. A. Ren, Z. X. Zhao, J. L. Luo, N. L. Wang, X. C. Wang, Q. Q. Liu, C. Q. Jin, C. T. Lin, Guo-qing Zheng

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 72 ( 5 ) 492 - 496 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

We present extensive (75)As NMR and NQR data on the superconducting arsenides PrFeAs(0.89)F(0.11) (T(c) = 45 K), LaFeAsO(0.92)F(0.08) (T(c) = 27 K), LiFeAs (T(c) = 17 K) and Ba(0.72)K(0.28)Fe(2)As(2) (T(c) = 31.5 K) single crystal, and compare with the nickel analog LaNiAsO(0.9)F(0.1) (T(c) = 4.0 K). In contrast to LaNiAsO(0.9)F(0.1) where the superconducting gap is shown to be isotropic, the spin lattice relaxation rate 1/T(1) in the Fe-arsenides decreases below T(c) with no coherence peak and shows a step-wise variation at low temperatures. The Knight shift decreases below T(c) and shows a step-wise T variation as well. These results indicate spin-singlet superconductivity with multiple gaps in the Fe-arsenides. The Fe antiferromagnetic spin fluctuations are anisotropic and weaker compared to underdoped copper-oxides or cobalt-oxide superconductors, while there is no significant electron correlations in LaNiAsO(0.9)F(0.1). We will discuss the implications of these results and highlight the importance of the Fermi surface topology. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2010.10.038

Theory of an inherent spin-density-wave instability due to vortices in superconductors with strong Pauli effects 査読

Kenta M. Suzuki, Masanori Ichioka, Kazushige Machida

PHYSICAL REVIEW B 83 ( 14 ) 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

A spin-density-wave (SDW) instability mechanism enhanced by vortices under fields is proposed to explain the high field and low-temperature phase in CeCoIn5. In the vortex state strong Pauli effect and nodal gap conspire to enhance the momentum-resolved density of states over the normal state value exclusively along the nodal direction, providing a favorable nesting condition for SDW with Q = (2k(F), 2k(F), 0.5) only at high fields (H). We can consistently understand observed mysteries of the field-induced SDW confined below H-c2, such as facts that Q is directed to the nodal direction independent of H, SDW diminishes under tilting field from the ab plane, and the SDW transition line in (H, T) has a positive slope.

DOI： 10.1103/PhysRevB.83.140503

Majorana surface states of superfluid He-3 A and B phases in a slab 査読

Y. Tsutsumi, M. Ichioka, K. Machida

PHYSICAL REVIEW B 83 ( 9 ) 2011年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Motivated by experiments on the superfluid He-3 confined in a thin slab, we design a concrete experimental setup for observing the Majorana surface states. We solve the quasiclassical Eilenberger equation, which is quantitatively reliable, to evaluate several quantities, such as local density of states (LDOS), mass current for the A phase, and spin current for the B phase. In connection with realistic slab samples, we consider the upper and lower surfaces and the side edges including the corners with several thicknesses. Consequently, the influence on the Majorana zero modes from the spatial variation of the l vector for the A phase in thick slabs and the energy splitting of the zero-energy quasiparticles for the B phase confined in thin slabs are demonstrated. The corner of slabs in the B phase is accompanied by the unique zero-energy LDOS of corner modes. On the basis of the quantitative calculation, we propose several feasible and verifiable experiments to check the existence of the Majorana surface states, such as the measurement of specific heat, edge current, and anisotropic spin susceptibility.

DOI： 10.1103/PhysRevB.83.094510

Majorana Edge Modes of Superfluid He-3 A- and B-Phases 査読

Y. Tsutsumi, T. Mizushima, M. Ichioka, K. Machida

JOURNAL OF LOW TEMPERATURE PHYSICS 162 ( 3-4 ) 196 - 203 2011年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER/PLENUM PUBLISHERS

Motivated by a recent experiment on the superfluid He-3 confined in a thin slab, we discuss the Majorana edge modes under the experimental situation. We solve the quasi-classical Eilenberger equation, which is quantitatively reliable, to evaluate several observables, such as local density of states, mass current for the A-phase, and spin current for the B-phase. On the basis of the quantitative calculation, we propose several experiments to check the existence of the Majorana modes.

DOI： 10.1007/s10909-010-0313-1

Lower Critical Field H-c1(T) and Pairing Symmetry Based on Eilenberger Theory 査読

Takanobu Akiyama, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 ( 1 ) 2011年1月

Vortex lattice transformation in d-wave superconductors with Pauli paramagnetic effect 査読

Kenta M. Suzuki, Masanori Ichioka, Kazushige Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 S564 - S565 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

By self-consistently solving the Eilenberger equations in a vortex state, we quantitatively evaluate the free energy for various lattice configurations of the d-wave superconductor under applied magnetic fields along to the c-axis, and discuss the dependence of stable configuration on the paramagnetic effect. By the paramagnetic effect, though the distribution of zero energy local density of states does not extend to the nodal direction above the middle fields, it still has good connection with vortex cores at the nodal directions. Then it makes square vortex lattice stable. We show that there is a first-order orientational transition before rocking into the square vortex lattice at low fields. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.11.081

As-75 NMR studies of superconducting Ba0.72K0.28Fe2As2 査読

Z. Li, K. Matano, D. L. Sun, G. L. Sun, C. T. Lin, M. Ichioka, G. -Q. Zheng

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 S495 - S496 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

We have performed As-75 nuclear magnetic resonance measurements on a single crystal of the hole-doped superconductor Ba0.72K0.28Fe2As2 (T-c = 31.5 K). The spin-lattice relaxation rate 1/T-1 decreases below T-c with no coherence peak and shows a step-wise variation at low temperatures, which is indicative of multiple superconducting gaps. In the normal state, we find that Fe antiferromagnetic spin fluctuations are anisotropic. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.11.174

Theory of superconducting symmetry in vortex lattice state 査読

Takehito Yokoyama, Masanori Ichioka, Yukio Tanaka

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 S886 - S887 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

We investigate symmetry of pairing correlation in vortex lattice state, and explain the electronic structure in this state in terms of pairing symmetry. We find that only odd-frequency pairing is present at the core centers, while at the midpoint of the vortex lines, only even-frequency pairing exists. Thus, the odd- and even-frequency pairings also form the lattice in the vortex lattice state. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.10.108

Majorana Edge Modes of Superfluid He-3 A-Phase in a Slab 査読

Yasumasa Tsutsumi, Takeshi Mizushima, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 11 ) 2010年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Motivated by a recent experiment on the superfluid He-3 A-phase with a chiral p-wave pairing confined in a thin slab, we propose designing a concrete experimental setup for observing the Majorana edge modes that appear around the circumference edge region. We solve the quasi-classical Eilenberger equation, which is quantitatively reliable, to evaluate several observables. To derive the property inherent to the Majorana edge state, the full quantum mechanical Bogoliubov-de Gennes equation is solved in this setting. On the basis of the results obtained, we perform decisive experiments to check the Majorana nature.

DOI： 10.1143/JPSJ.79.113601

Theory of pairing symmetry in the vortex states 査読

Takehito Yokoyama, Masanori Ichioka, Yukio Tanaka, Alexander Golubov

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 ( 19 ) 766 - 770 2010年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

We investigate pairing symmetry in an Abrikosov vortex and vortex lattice. It is shown that the Cooper pair wave function at the center of an Abrikosov vortex with vorticity m has a different parity with respect to frequency from that in the bulk if m is an odd number, while it has the same parity if m is an even number. As a result, in a conventional vortex with m = 1, the local density of states at the Fermi energy has a maximum (minimum) at the center of the vortex core in an even (odd)-frequency superconductor. In the vortex lattice of s-wave superconductor, we find that only odd-frequency pairing is present at the core centers, while at the midpoint of the vortex lines, only even-frequency pairing exists. Thus, the odd and even-frequency pairings also form the lattice in the vortex lattice state. We also propose a scanning tunneling microscope experiment using a superconducting tip to explore odd-frequency superconductivity. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2010.02.084

Skyrmion lattice and intrinsic angular momentum effect in the A phase of superfluid He-3 under rotation 査読

Masanori Ichioka, Takeshi Mizushima, Kazushige Machida

PHYSICAL REVIEW B 82 ( 9 ) 2010年9月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

As an example of the skyrmion lattice, the structure of Mermin-Ho vortex lattice in superfluids He-3 is studied by self-consistent Eilenberger theory and by Bogoliubov-de Gennes theory. We identify how the intrinsic orbital angular momentum 1 of p-wave Cooper pairs contributes to spatial structures of the pair potential, current flow, and quasiparticle states. There are two types of vortices depending on the 1 direction relative to rotation. Only one of them has zero-energy bound states appearing even in coreless vortices due to intrinsic topological reasons.

DOI： 10.1103/PhysRevB.82.094516

Vortex State and Field-Angle Resolved Specific Heat Oscillation for H parallel to ab in d-Wave Superconductors 査読

Masayuki Hiragi, Kenta M. Suzuki, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 9 ) 2010年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

When magnetic field is applied parallel to the ab-plane in d(x2-y2)-wave superconductors, the transition of a stable vortex lattice structure, the spatial structure of local density of states, and the specific heat oscillation induced by rotation of the magnetic field orientation are investigated by quantitative calculations based on the self-consistent Eilenberger theory. We estimate how the vortex state changes depending on the relative angle between the node direction of the superconducting gap and magnetic field orientation. To reproduce the sign change of specific heat oscillation observed in CeCoIn5, our study is perfomed by including a strong paramagnetic effect. The quantitative theoretical calculations give decisive information to analyze the experimental data on the field-angle dependence, and establish the angle-resolved specific heat experiment as a spectroscopic means to identify the node position of the superconducting gap.

DOI： 10.1143/JPSJ.79.094709

As-75 NQR and NMR Studies of Superconductivity and Electron Correlations in Iron Arsenide LiFeAs 査読

Zheng Li, Yosuke Ooe, Xian-Cheng Wang, Qing-Qing Liu, Chang-Qing Jin, Masanori Ichioka, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 8 ) 2010年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We report the As-75-NQR and NMR studies on the iron arsenide superconductor LiFeAs with T-c similar to 17 K. The spin lattice relaxation rate, 1/T-1, decreases below T-c without a coherence peak, and can be fitted by gaps with s(+/-)-wave symmetry in the presence of impurity scattering. In the normal state, both 1/T1T and the Knight shift decrease with decreasing temperature but become constant below T <= 50 K. Estimate of the Korringa ratio shows that the spin correlations are weaker than those in other families of iron arsenides, which may account for the lower T-c in this material.

DOI： 10.1143/JPSJ.79.083702

Theory of Pairing Symmetry in Fulde-Ferrell-Larkin-Ovchinnikov Vortex State and Vortex Lattice 査読

Takehito Yokoyama, Masanori Ichioka, Yukio Tanaka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 3 ) 2010年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We investigate the pairing symmetry of induced superconductivity in two systems, namely, (i) the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex state and (ii) vortex lattice state without FFLO modulation, and explain the electronic structure in these states in terms of pairing symmetry. We analytically show that, at the intersection point of the FFLO nodal plane and vortex line, only even-frequency pairing is present if the Zeeman splitting is negligible. With increasing Zeeman splitting, odd-frequency pairing emerges at such a point. In the vortex lattice, we find that only odd-frequency pairing is present at core centers, while at the midpoint of vortex lines, only even-frequency pairing exists.

DOI： 10.1143/JPSJ.79.034702

Textures and Exotic Vortices in Neutral Fermion Superfluids 査読

K. Machida, Y. Tsutsumi, T. Kawakami, H. M. Adachi, J. A. M. Huhtamaki, T. Mizushima, M. Ichioka

JOURNAL OF LOW TEMPERATURE PHYSICS 158 ( 3-4 ) 377 - 383 2010年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER/PLENUM PUBLISHERS

There has been intense interest in various Fermion superfluids in neutral atom liquids and gases, including chiral p-wave pairing in He-3-A phase and Feshbach-resonanced Li-6 atom gases and d-wave pairing in atom gases. It is particularly interesting to find exotic vortices and associated low-lying Fermionic excitations under rotation. Here we report on our efforts of those topics: (1) Majorana Fermion in chiral superfluids near a p-wave Feshbach resonance. (2) Possible half-quantum vortices in p-wave superfluids of trapped Fermion atom gases. (3) Stability of a half-quantum vortex in rotating superfluid He-3-A between parallel plates. (4) Majorana bound state in rotating superfluid He-3-A between parallel plates. (5) Non-Abelian Fractional vortex in d-wave Feshbach resonance superfluids. We will summarize some of those works in a coherent manner in order to bridge the understanding between cold atom community and superfluid He-3 community by stressing the importance of cross fertilization between them.

DOI： 10.1007/s10909-009-0002-0

Sign Reversal of Field-Angle Resolved Heat Capacity Oscillations in a Heavy Fermion Superconductor CeCoIn5 and dx2-y2 Pairing Symmetry 査読

K. An, T. Sakakibara, R. Settai, Y. Onuki, M. Hiragi, M. Ichioka, K. Machida

PHYSICAL REVIEW LETTERS 104 ( 3 ) 2010年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

To identify the superconducting gap symmetry in CeCoIn5 (T-c = 2.3 K), we measured the angle-resolved specific heat (C-phi) in a field rotated around the c axis down to a very low temperature, 0.05T(c), and made detailed theoretical calculations. In a field of 1 T, a sign reversal of the fourfold angular oscillation in C-phi was observed at T similar or equal to 0.1T(c) upon entering a quasiclassical regime where the maximum of C-phi corresponds to the antinodal direction, coinciding with the angle-resolved density of states (ADOS) calculation. The C-phi behavior, which exhibits minima along the [110] directions, unambiguously allows us to conclude d(x2-y2) symmetry of this system. The ADOS-quasiclassical region is confined to a narrow T and H domain within T/T-c similar to 0.1 and 1.5 T (0.13H(c2)).

DOI： 10.1103/PhysRevLett.104.037002

Generic First-Order Orientation Transition of Vortex Lattices in Type II Superconductors 査読

Kenta M. Suzuki, Kenji Inoue, Predrag Miranovic, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 1 ) 2010年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The first-order transition of vortex lattices (VLs) observed in various superconductors with fourfold symmetry is explained microscopically by quasi-classical Eilenberger theory combined with nonlocal London theory. This transition is intrinsic in the generic successive VL phase transition due to either gap anisotropy or Fermi velocity anisotropy. This is also suggested by the electronic states around vortices. Ultimately, the origin of this phenomenon is attributed to somewhat hidden frustrations of a spontaneous symmetry-broken hexagonal VL in the underlying fourfold crystalline symmetry.

DOI： 10.1143/JPSJ.79.013702

Inherent spin density wave instability by vortices in superconductors with strong Pauli effects

Masanori Ichioka

ArXiv 2010年

Anisotropic spin fluctuations and multiple superconducting gaps in hole-doped Ba0.72K0.28Fe2As2: NMR in a single crystal 査読

K. Matano, Z. Li, G. L. Sun, D. L. Sun, C. T. Lin, M. Ichioka, Guo-Qing Zheng

EPL 87 ( 2 ) 27012, 1-6 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

We report the As-75-NMR study on a single crystal of the hole-doped iron-pnictide superconductor Ba0.72K0.28Fe2As2 (T-c = 31.5 K). We find that the Fe antiferromagnetic spin fluctuations are anisotropic and are weaker compared to underdoped copper-oxides or cobalt-oxide superconductors. The spin lattice relaxation rate 1/T-1 decreases below T-c with no coherence peak and shows a stepwise variation at low temperatures, which is indicative of multiple superconducting gaps, as in the electron-doped Pr(La) FeAsO1-xFx. Furthermore, no evidence was obtained for a microscopic coexistence of a long-range magnetic order and superconductivity. Copyright (C) EPLA, 2009

DOI： 10.1209/0295-5075/87/27012

Singular and Non-singular Vortices and Their Excitation Spectra of Neutral Fermi Superfluids in Restricted Geometries 査読

K. Machida, Y. Tsutsumi, T. Kawakami, T. Mizushima, M. Ichioka, M. Takahashi

25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 3 150 ( 3 ) 032049, 1-4 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

We study stable vortices and their bound excitation spectra in superfluid (3)He-A phase under restricted geometries. By choosing appropriate geometry we can control the (l) over right arrow -vector and (d) over right arrow -vector of the A phase order parameter (OP), making it possible to select a particular vortex among a variety of singular or non-singular vortices. This tunability through the boundary condition and external field is demonstrated to be useful. Here we take up two examples of the restricted geometries under rotation: A narrow cylinder whose radius is 50 mu m under field parallel to the rotation axis and thin film configuration sandwiched by parallel plates whose gap is an order of mu m or less. We examine the ongoing experiment by rotating cryostat at ISSP, University of Tokyo, reporting on new vortex state for a cylinder in a slow rotation speed region near T(c). For parallel plates in a field parallel to the film surface we analyze the conditions under which singular vortex is stable. This study allows us to examine experimental realization of so-called Majorana zero energy state bound in a core in (3)He-A chiral phase.

DOI： 10.1088/1742-6596/150/3/032049

p波超流動体の量子渦に潜むマヨラナ型準粒子

水島健, 市岡優典, 町田一成

日本物理学会誌 64 ( 11 ) 836 - 840 2009年

Majorana Fermions in Quantized Vortices of p-Wave Superfluids 査読

Takeshi Mizushima, Masanori Ichioka, Kazushige Machida

Butsuri 64 836 - 840 2009年

Flux line lattice form factor and paramagnetic effects in type II superconductors 査読

Masanori Ichioka, Kazushige Machida

25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 150 ( 5 ) 052074, 1-4 2009年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

Based on the quasiclassical Eilenberger theory, we investigate the vortex structure in type II superconductors with strong Pauli-paramagnetic contributions due to the Zeeman effect. We quantitatively study how the paramagnetic effect suppresses the superconductivity, and evaluate the flux line lattice (FLL) form factor from the calculated internal field distribution both in the s-wave and d-wave pairings. When the paramagnetic effects are strong, the intensity of the FLL form factor increases toward H(c2) as a function of an applied field, instead of exponential decay. This anomalous field dependence is due to the induced paramagnetic moments around the vortex core. We discuss the anomalous field-dependence of the FLL form factor observed by the small angle neutron scattering in CeCoIn(5).

DOI： 10.1088/1742-6596/150/5/052074

Anisotropic spin fluctuations and multiple superconducting gaps in hole-doped Ba_0.7K_0.3Fe_2As_2: NMR in a single crystal

Masanori Ichioka

ArXiv 2009年

Role of the Majorana Fermion and the Edge Mode in Chiral Superfluidity near a p-Wave Feshbach Resonance 査読

T. Mizushima, M. Ichioka, K. Machida

PHYSICAL REVIEW LETTERS 101 ( 15 ) 150409 1-4 2008年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The visualization of chiral p-wave superfluidity in Fermi gases near p-wave Feshbach resonances is theoretically examined. It is proposed that the superfluidity becomes detectable in the entire BCS-BEC regimes through (i) vortex visualization by the density depletion inside the vortex core and (ii) intrinsic angular momentum in vortex-free states. It is revealed that both (i) and (ii) are closely connected with the Majorana zero energy mode of the vortex core and the edge mode, which survive until the strong coupling BCS regime is approached from the weak coupling limit and vanish in the Bose-Einstein condensation regime.

DOI： 10.1103/PhysRevLett.101.150409

Majorana bound state in rotating superfluid (3)He-A between parallel plates 査読

Y. Tsutsumi, T. Kawakami, T. Mizushima, M. Ichioka, K. Machida

PHYSICAL REVIEW LETTERS 101 ( 13 ) 135302 1-4 2008年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

A concrete and experimentally feasible example for testing the putative Majorana zero-energy state bound in a vortex is theoretically proposed for a parallel plate geometry of superfluid (3)He-A phase. We examine the experimental setup in connection with ongoing rotating cryostat experiments. The theoretical analysis is based on the well-established Ginzburg-Landau functional, supplemented by microscopic calculations of the Bogoliubov-de Gennes equation, both of which allow the precise location of the parameter regions of the Majorana state to be found in realistic situations.

DOI： 10.1103/PhysRevLett.101.135302

Magnetization profile and core-level spectroscopy in a multiply quantized vortex of imbalanced Fermi superfluids 査読

K. M. Suzuki, T. Mizushima, M. Ichioka, K. Machida

Physical Review A - Atomic, Molecular, and Optical Physics 77 ( 6 ) 2008年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The core structure of multiply quantized vortices is theoretically investigated in a fermionic superfluid near Feshbach resonance. Under population imbalance in two hyperfine spin states, the vortex core is filled in by the "paramagnetic moment." Here, we find the spatial oscillation of the magnetization inside the core sensitively due to the topological structure of the pairing field, in the range from the weak-coupling regime to the unitary limit. This magnetization inside the giant core reveals the winding number of the vortex and directly results from the low-lying quasiparticle states bound inside the core. It is therefore proposed that the density profile experiment using phase contrast imaging can provide the spectroscopy of novel core level structures in giant vortices. To help understand these outcomes, we also derive an analytic solution for the low-lying quasiparticle states inside the core of a multiply quantized vortex. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevA.77.063617

Magnetic field dependence of low-temperature specific heat in Sr(2)RuO(4) 査読

K. Machida, M. Ichioka

PHYSICAL REVIEW B 77 ( 18 ) 184515 1 2008年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The magnetic field (H) dependence of the Sommerfeld coefficient gamma(H) of the low-temperature specific heat in Sr(2)RuO(4) is analyzed by numerically solving the microscopic Eilenberger equation. By taking account of the strong Pauli-paramagnetic effect, we find that gamma(H) exhibits a systematic change from a concave function root H to a convex function H(alpha)(alpha>1) at high fields when the orientation of the magnetic field is varied, explaining experimental results. The magnetization is found to be consistent with this behavior. This implies either singlet pairing or triplet pairing with the d vector locked in the basal plane. Based on this conclusion, we explain other properties of this compound.

DOI： 10.1103/PhysRevB.77.184515

Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu(2)Si(2) 査読

K. Yano, T. Sakakibara, T. Tayama, M. Yokoyama, H. Amitsuka, Y. Homma, P. Miranovic, M. Ichioka, Y. Tsutsumi, K. Machida

PHYSICAL REVIEW LETTERS 100 ( 1 ) 017004 1-4 2008年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

To identify the superconducting gap structure in URu(2)Si(2), we perform field-angle-dependent specific heat measurements for the two principal orientations in addition to field rotations, and a theoretical analysis based on microscopic calculations. The Sommerfeld coefficient gamma(H)'s in the mixed state exhibit a distinctly different field dependence. This comes from point nodes and the substantial Pauli paramagnetic effect of URu(2)Si(2). These two features combined give rise to a consistent picture of superconducting properties, including a possible first order transition of H(c2) at low temperatures.

DOI： 10.1103/PhysRevLett.100.017004

LITTLE-PARKS OSCILLATIONS IN CHIRAL p-WAVE SUPERCONDUCTING RINGS 査読

M. Takigawa, Y. Asano, M. Ichioka

CONTROLLABLE QUANTUM STATES: MESOSCOPIC SUPERCONDUCTIVITY AND SPRINTRONICS 155 - + 2008年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：WORLD SCIENTIFIC PUBL CO PTE LTD

Oscillations of critical temperature T-c of superconducting rings under the applied magnetic field are studied based on the time-dependent Ginzburg-Landau theory. We analyze the Little-Parks oscillations in s-wave and chiral p-wave superconductors. In s-wave superconductor, we confirm clear oscillations in T-c. When phase winding numbers around a bole change, T-c takes local minimum. Period of oscillation behaviors depends oil a shape of rings. The conventional Little-Parks oscillations do not appear in chiral p-wave superconductor because of the unusual flux penetration in superconducting ring.

DOI： 10.1142/9789812814623_0025

Electronic thermal conductivity in a superconducting vortex state 査読

H. Adachi, P. Miranovic, M. Ichioka, K. Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 463 36 - 39 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The longitudinal component of the electronic thermal conductivity kappa(xx) in a superconducting vortex state is calculated as a function of magnetic field B. Calculations are performed by taking account of the spatial dependence of normal Green's function g, which was neglected in the previous studies using the Brandt-Pesch-Tewordt method. We discuss the possibility of using kappa(xx)(B) as a probe of the pair potential symmetry. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2007.03.433

Pauli paramagnetic effects on vortices in superconducting TmNi2B2C 査読

L. DeBeer-Schmitt, M. R. Eskildsen, M. Ichioka, K. Machida, N. Jenkins, C. D. Dewhurst, A. B. Abrahamsen, S. L. Bud'ko, P. C. Canfield

PHYSICAL REVIEW LETTERS 99 ( 16 ) 167001 1-4 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The magnetic field distribution around the vortices in TmNi2B2C in the paramagnetic phase was studied experimentally as well as theoretically. The vortex form factor, measured by small-angle neutron scattering, is found to be field independent up to 0.6H(c2) followed by a sharp decrease at higher fields. The data are fitted well by solutions to the Eilenberger equations when paramagnetic effects due to the exchange interaction with the localized 4f Tm moments are included. The induced paramagnetic moments around the vortex cores act to maintain the field contrast probed by the form factor.

DOI： 10.1103/PhysRevLett.99.167001

Imbalanced superfluid phase of a trapped fermi gas in the BCS-BEC crossover regime 査読

Takeshi Mizushima, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 10 ) 104006 1-15 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We theoretically investigate the ground state of trapped neutral fermions with population imbalance in the BCS-BEC crossover regime. On the basis of the single-channel Hamiltonian, we perform full numerical calculations of the Bogoliubov-de Gennes equation coupled with the regularized gap and number equations. The zero-temperature phase diagram in the crossover regime is presented, where the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state governs the weak-coupling BCS region of a resonance. It is found that the FFLO oscillation vanishes in the BEC side, in which the system under population imbalance turns into a phase separation (PS) between locally binding superfluid and fully polarized spin domains. We also demonstrate numerical calculations with a large particle number O(10(5)), comparable to that observed in recent experiments. The resulting density profile on a resonance yields the PS, which is in good agreement with the recent experiments, while the FFLO modulation exists in the pairing field. It is also proposed that the most favorable location for the detection of the FFLO oscillation is in the vicinity of the critical population imbalance in the weak coupling BCS regime, where the oscillation periodicity becomes much larger than the interparticle spacing. Finally, we analyze the radio-frequency (RF) spectroscopy in the imbalanced system. The clear difference in the RF spectroscopy between BCS and BEC sides reveals the structure of the pairing field and local "magnetization".

DOI： 10.1143/JPSJ.76.104006

Vortex states in superconductors with strong Pauli-paramagnetic effect 査読

Masanori Ichioka, Kazushige Machida

PHYSICAL REVIEW B 76 ( 6 ) 064502 1-7 2007年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Using quasiclassical theory, we analyze the vortex structure of strong-paramagnetic superconductors. There, induced paramagnetic moments are accumulated exclusively around the vortex core. We quantitatively evaluate the significant paramagnetic effect in the H dependence of various quantities, such as low temperature specific heat, Knight shift, magnetization, and the flux line lattice (FLL) form factor. The anomalous H dependence of the FLL form factor observed by the small angle neutron scattering in CeCoIn5 is attributable to the large paramagnetic contribution.

DOI： 10.1103/PhysRevB.76.064502

Visibility of vortex core in fermionic superfluid with population imbalance 査読

M. Takahashi, T. Mizushima, K. Machida, M. Ichioka

JOURNAL OF LOW TEMPERATURE PHYSICS 148 ( 3-4 ) 423 - 427 2007年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER/PLENUM PUBLISHERS

In Fermionic superfluids with a vortex, at T=0, the depletion of the atomic density appears in the core region, which is strongly associated with the discreteness of the core-bound state, called the Caroli-de Gennes-Matricon state. In imbalanced superfluid, however, it is found by the microscopic study based on the Bogoliubov-de Gennes approximation that this quantum depletion is progressively filled out in majority spin species as population imbalance increases. In contrast, the minority species keeps the depletion, which enables the direct observation of "superfluidity", because the quantized vortex is a hallmark of superfluidity.

DOI： 10.1007/s10909-007-9399-5

Vortex state in a Fulde-Ferrell-Larkin-Ovchinnikov superconductor based on quasiclassical theory 査読

Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

PHYSICAL REVIEW B 76 ( 1 ) 014503 1-10 2007年7月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We investigate the vortex state with Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulations suggested for a high-field phase of CeCoIn5. On the basis of quasiclassical Eilenberger theory, we calculate the three-dimensional structure of pair potentials, internal magnetic fields, paramagnetic moments, and electronic states for s-wave and d-wave pairings comparatively. The pi-phase shift of the pair potential at the FFLO nodal plane or at the vortex core induces sharp peak states in the local density of states and enhances the local paramagnetic moment. We also discuss the NMR spectrum and neutron scattering as methods to detect the FFLO structure.

DOI： 10.1103/PhysRevB.76.014503

Quasi-classical calculation of the mixed-state thermal conductivity in s- and d-wave superconductors 査読

Hiroto Adachi, Predrag Miranovic, Masanori Ichioka, Kazushige Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 6 ) 064708 1-7 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

To see how superconducting gap structures affect the longitudinal component of mixed-state thermal conductivity K-xx(B), the magnetic-field dependences of K-xx(B) in s- and d-wave superconductors are investigated. Calculations are performed on the basis of the quasi-classical theory of superconductivity by fully taking account of the spatial variation of the normal Green's function, neglected in previous works, by the Brandt-Pesch-Tewordt approximation. On the basis of our result, we discuss the possibility of K-xx(B) measurement as a method of probing the gap structure.

DOI： 10.1143/JPSJ.76.064708

Vortex state in FFLO superconductors 査読

Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 593 - 595 2007年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Based on the quasiclassical theory, we investigate the vortex structure in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state suggested for the high. field phase of CeCoIn5. We show that the paramagnetic moments are enhanced at the vortex line and at the nodal plane of the FFLO modulation, and discuss the double peak structure of the NMR spectrum in the FFLO state. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.237

Quasiclassical calculation of the quasiparticle thermal conductivity in a mixed state 査読

Hiroto Adachi, Predrag Miranovic, Masanori Ichioka, Kazushige Machida

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 640 - 642 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We report the result of calculation of the quasiparticle thermal conductivity kappa(xx)(del T perpendicular to B) in the vortex state of a two-dimensional superconductor. We compute k(xx) for both s-wave and d-wave superconductors, taking account of the spatial dependence of normal Green's function g, which is neglected in the previous studies using the Brandt-Pesch-Tewordt (BPT) method. Our results indicate that k(xx) based on the BPT method is slightly underestimated due to its incoherent spatial averaging procedure. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.102

Macroscopic manifestations of broken inversion symmetry in noncentrosymmetric superconductors with applied magnetic field 査読

Masatosi Oka, Masanori Ichioka, Kazushige Machida

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 575 - 577 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We numerically investigate paramagnetic properties in noncentrosymmetric superconductors under applied magnetic fields, based on the time-dependent Ginzburg-Landau theory including the Pauli paramagnetic effect and the Rashba interaction. When an applied field is perpendicular to the polar axis, the paramagnetic effect breaks centrosymmetry in the Meissner state and cylindrical symmetry in the vortices, as macroscopic manifestations of broken inversion symmetry in the spatial structures of the screening current and the penetrating field. The paramagnetic supercurrent exists even at the vortex center by their asymmetric properties, therefore the flux flow is spontaneously induced without applying external currents. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2006.10.153

Theory of tunneling spectroscopy in the Larkin-Ovchinnikov state 査読

Yukio Tanaka, Yasuhiro Asano, Masanori Ichioka, Satoshi Kashiwaya

PHYSICAL REVIEW LETTERS 98 ( 7 ) 077001 1-4 2007年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We present a theory of tunneling spectroscopy for normal metal/Larkin-Ovchinnikov state junctions in which the spatial periodic modulation in the pair potential amplitude is taken into account. The tunneling spectra show the characteristic line shapes reflecting the minigap structures under the periodic pair potentials depending on the boundary condition of the pair potentials at the junction interface. These features are qualitatively different from the tunneling spectra of the Fulde-Ferrell state. We propose an experimental setup which identifies the superconducting state of CeCoIn5.

DOI： 10.1103/PhysRevLett.98.077001

Thermal conductivity in the vortex state of s-wave and d-wave superconductors 査読

Miranović P, Adachi H, Ichioka M, Machida K

AIP Conference Proceedings 899 630 - 630 2007年

Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu2Si2

Masanori Ichioka

ArXiv 2007年

Effect of the vortices on the nuclear spin relaxation rate in the unconventional pairing states of the organic superconductor (TMTSF)(2)PF6 査読

M. Takigawa, M. Ichioka, K. Kuroki, Y. Asano, Y. Tanaka

PHYSICAL REVIEW LETTERS 97 ( 18 ) 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

This Letter theoretically discusses quasiparticle states and nuclear spin relaxation rates T-1(-1) in the quasi-one-dimensional superconductor (TMTSF)(2)PF6 under a magnetic field applied parallel to the conduction chains. We study the effects of Josephson-type vortices on T-1(-1) by solving the Bogoliubov-de Gennes equation for p-, d- or f-wave pairing interactions. In the presence of line nodes in pairing functions, T-1(-1) is proportional to T in sufficiently low temperatures because quasiparticles induced by vortices at the Fermi energy relax spins. We also try to identify the pairing symmetry of (TMTSF)(2)PF6.

DOI： 10.1103/PhysRevLett.97.187002

Vortex-core structure in neutral fermion superfluids with population imbalance 査読

M. Takahashi, T. Mizushima, M. Ichioka, K. Machida

PHYSICAL REVIEW LETTERS 97 ( 18 ) 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Quantized vortex-core structure is theoretically investigated in fermion superfluids with population imbalance for two atom species of neutral atom clouds near a Feshbach resonance. In contrast with the vortex core in balance case where the quantum depletion makes a vortex visible through the density profile measurement, the vortex core is filled in and becomes less visible because the quantized discrete bound states are occupied exclusively by the majority species. Yet it is shown that the core can be visible through the minority density profile experiment using phase contrast imaging, revealing an interesting opportunity to examine low-lying fermionic core bound states unexplored so far.

DOI： 10.1103/PhysRevLett.97.180407

Electronic structure of vortex state in a FFLO superconductor 査読

Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 445 186 - 189 2006年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Vortex states in a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor are microscopically investigated by the quasi-classical Eilenberger theory. We calculate the spatial structure of the pair potential, paramagnetic magnetization (i.e., Knight shift in a magnetic field) and electronic states, including paramagnetic depairing effect in addition to the orbital depairing effect. Topologies of 2 pi phase winding at the vortex line and pi phase shift at the FFLO nodal plane affect the distribution of paramagnetic magnetization and low energy electronic states. We also discuss the NMR resonance line shape observed in the high field phase of CeCoIn5. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2006.03.111

Electronic structures and NMR T-1(-1) in quasi-one-dimensional organic superconductor (TMTSF)(2)PF6 査読

M. Takigawa, M. Ichioka, K. Kuroki, Y. Tanaka, Y. Asano

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 445 190 - 193 2006年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

On the basis of the Bogoliubov de Gennes theory, electronic structures around a vortex in quasi-one-dimensional organic superconductor (TMTSF)(2)PF6 are studied at the quarter-filling electron density in magnetic fields applied parallel to the conduction chain. We consider three pairing symmetries (d-, p- and f-wave) in superconductors. In d- and f-wave symmetries, nuclear relaxation rate T-1(-1) is proportional to temperatures because quasiparticles around the vortex relax spins. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2006.03.112

Ubiquitous V-shape density of states in a mixed state of clean limit type II superconductors 査読

N. Nakai, P. Miranovic, M. Ichioka, H. F. Hess, K. Uchiyama, H. Nishimori, S. Kaneko, N. Nishida, K. Machida

PHYSICAL REVIEW LETTERS 97 ( 14 ) 2006年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

It is demonstrated theoretically and experimentally that the low energy density of states N(E) is described by a singular V-shape form N(E)=N-0(H)+alpha vertical bar E vertical bar+O(E-2) for all clean superconductors in a vortex state, irrespective of the underlying gap structure. The linear term alpha|E| which has not been recognized so far is obtained by exactly evaluating the vortex contribution. Based on microscopic Eilenberger theory N(E) is evaluated for the isotropic gap, line, and point-node gaps to yield a V-shape N(E). Scanning tunneling spectroscopy-STM experiments on NbSe2 and YNi2B2C give direct evidence for this. We provide arguments on the significance of this finding and on the relevance to other experiments.

DOI： 10.1103/PhysRevLett.97.147001

Generic phase diagram of Fermion superfluids with population imbalance 査読

K. Machida, T. Mizushima, M. Ichioka

PHYSICAL REVIEW LETTERS 97 ( 12 ) 2006年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

It is shown by microscopic calculations for trapped imbalanced Fermi superfluids that the gap function always has sign changes, i.e., the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like state, up to a critical imbalance P(c), beyond which normal state becomes stable, at temperature T=0. A temperature-versus-pressure phase diagram is constructed, where the BCS state without sign change is stable only at T not equal 0. We reproduce the observed bimodality in the density profile to identify its origin and evaluate P(c) as functions of T and the coupling strength. These dependencies match with the recent experiments.

DOI： 10.1103/PhysRevLett.97.120407

Basal-Plane Magnetic Anisotropies of High-κ d-Wave Superconductors in a Mixed State: A Quasiclassical Approach 査読

H. Adachi, P. Miranovic, M. Ichioka, K. Machida

Journal of the Physical Society of Japan 75 ( 8 ) 2006年8月

Surface and vortex structures in noncentrosymmetric superconductors under applied magnetic fields 査読

Masatosi Oka, Masanori Ichioka, Kazushige Machida

PHYSICAL REVIEW B 73 ( 21 ) 2006年6月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

We investigate how the macroscopic spatial structure of broken inversion symmetry manifests in noncentrosymmetric superconductors, by the microscopic broken inversion symmetry of the crystal structure. Based on the time-dependent Ginzburg-Landau theory including the Pauli paramagnetic effect and the Rashba interaction, we demonstrate that the centrosymmetric structures of the internal field and the screening current are broken macroscopically. The flow structure of paramagnetic supercurrent spontaneously induces the flux flow without applying external currents.

DOI： 10.1103/PhysRevB.73.214509

Specific heat and low-lying excitations in the mixed state for a type-II superconductor 査読

N. Nakai, P. Miranovic, M. Ichioka, K. Machida

PHYSICAL REVIEW B 73 ( 17 ) 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

Low temperature behavior of the electronic specific heat C(T) in the mixed state is by the self-consistent calculation of the Eilenberger theory. In addition to the gamma T-term (gamma is a Sommerfeld coefficient), C(T) has a significant contribution of T-2-term intrinsic in the vortex state. We identify the origin of the T-2 term as (i) V-shape density of states in the vortex state and (ii) the Kramer-Pesch effect of vortex-core shrinking upon lowering T. These results for both full-gap and line-node cases reveal that the vortex core is a richer electronic structure beyond the normal core picture.

DOI： 10.1103/PhysRevB.73.172501

Fulde-Ferrell-Larkin-Ovchinnikov states in Fermi gases with unequal populations 査読

T. Mizushima, K. Machida, M. Ichioka

LOW TEMPERATURE PHYSICS, PTS A AND B 850 79 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AMER INST PHYSICS

We theoretically investigate the microscopic structure of neutral Fermionic systems with unequal atomic populations. By using fully microscopic Bogoliubov-de Gennes framework, we study on the vortex structure in a single-vortex state with and without the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulation of the pairing field. It is found that the novel local density of states structure appears at intersection point of the FFLO nodal plane and the vortex line, which reflects the topological structure of the pairing field.

DOI： 10.1063/1.2354613

Electronic structure of vortex in the FFLO superconducting state 査読

Masanori Ichioka, Hiroto Adachi, Takeshi Mizushima, Kazushige Machida

LOW TEMPERATURE PHYSICS, PTS A AND B 850 725 - 728 2006年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AMER INST PHYSICS

Based on the quasiclassical theory, we investigate the vortex structure in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state suggested to exist for the high field phase of CeCoIn5. The pair potential has 2 pi-phase winding around the vortex line, and x-phase shift at the nodal plane of the FFLO modulation. These topologies of the phase structure affect the distribution of paramagnetic moment and low energy electronic states. We also discuss the resonance line shape of the Knight shift in the FFLO state.

DOI： 10.1063/1.2354912

非対称粒子分布を持つフェルミ原子気体における FFLO 状態実現の可能性

水島健, 市岡優典, 町田一成

素粒子論研究 114 ( 3 ) C5 - C12 2006年

Theory of gap-node detection by angle-resolved specific heat measurement 査読

P Miranovic, M Ichioka, K Machida, N Nakai

JOURNAL OF PHYSICS-CONDENSED MATTER 17 ( 50 ) 7971 - 7980 2005年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

The specific heat oscillation in the mixed state of type II superconductors is studied theoretically when rotating a field within a plane containing a gap minimum and maximum. The calculations are performed microscopically by solving the quasi-classical Eilenberger equation for vortex lattices. The field dependence of the oscillation amplitude can discriminate between the nodal and anisotropic gap with a finite minimum and the oscillation phase gives the gap minimum position on the Fermi surface. These also provide a way to separate out the anisotropic behaviour due to the Fermi velocity.

DOI： 10.1088/0953-8984/17/50/015

Electronic structure and spontaneous internal field around nonmagnetic impurities in spin-triplet chiral p-wave superconductors 査読

M Takigawa, M Ichioka, K Kuroki, Y Tanaka

PHYSICAL REVIEW B 72 ( 22 ) 2005年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The electronic structure around an impurity in spin-triplet p-wave superconductors is studied by the Bogoliubov-de Gennes theory on a tight-binding model, where we have chosen sin p(x)+i sin p(y)-wave or sin(p(x)+p(y))+i sin(-p(x)+p(y))-wave states, which are considered to be candidates for the pairing state in Sr2RuO4. We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between the two types of pairing. We propose that it is possible to discriminate the two pairing states by studying the spatial dependence of the magnetic field around a pair of impurities.

DOI： 10.1103/PhysRevB.72.224501

Spontaneous internal field around the non-magnetic impurity in spin-triplet p-wave superconductivity 査読

A Takigawa, M Ichioka, K Kuroki, Y Tanaka

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 29 ( 3-4 ) 619 - 623 2005年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The electronic structure around an impurity in spin triplet p-wave superconductors is investigated by the Bogoliubov-de Gennes theory on a tight-binding model. We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between sin p(x) + i sin p(y)-wave and sin(p(x) +p(y)) - i sin(-p(x) +p(y))-wave superconducting states. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2005.06.040

Vortex core states in high-T-c superconductors with induced incommensurate spin and charge density waves 査読

M Ichioka, M Takigawa, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 426 28 - 35 2005年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We investigate the change of the vortex structure in the presence of the induced stripe or checkerboard pattern modulation of the incommensurate spin density wave (SDW) and charge density wave (CDW) around the vortex core. The order parameter and the quasiparticle structure in the vortex lattice state are calculated by Bogoliubov-de Gennes theory on a two-dimensional Hubbard model with nearest-neighbor site pairing interaction. By the induced SDW and CDW, low-energy excitations around the vortex core are suppressed, producing "empty core" structure, as observed by the scanning tunneling microscopy. In the relation to these quasiparticle structures, we discuss the site-selective nuclear spin relaxation time T, and thermal conductivity in the vortex state. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2005.01.016

Topological structure of a vortex in the Fulde-Ferrell-Larkin-Ovchinnikov state 査読

T Mizushima, K Machida, M Ichioka

PHYSICAL REVIEW LETTERS 95 ( 11 ) 2005年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We find theoretically that the vortex core in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is quite different from the ordinary core for a simple topological reason. The intersection point of a vortex and nodal plane of the FFLO state empties the excess spins. This leads to observable consequences in the spatial structure of the spontaneous magnetization. We analyze this topological structure based on the low lying excitation spectrum by solving a microscopic Bogoliubov-de Gennes equation to clarify its physical origin.

DOI： 10.1103/PhysRevLett.95.117003

Theoretical study on the field dependence of the zero energy density of states in an anisotropic gap superconductors 査読

N Nakai, P Miranovic, M Ichioka, K Machida

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 ( 8-9 ) 1362 - 1364 2005年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Based on the quasi-classical theory, we calculate the zero energy density of states N(B) in the mixed state for a type 11 superconductor. N(B) is related to the sommerfeld coefficient gamma(B), which gives us useful information for a superconducting gap. The linear portion in gamma(B) relative to B,2 and its slope in a low field reflect the gap anisotropy, so that we can distinguish the nodal gap and the anisotropic full gap, and estimate the magnitude of the gap anisotropy. (c) 2005 Published by Elsevier Ltd.

DOI： 10.1016/j.jpcs.2005.05.011

Mixed-state thermodynamics of superconductors with moderately large paramagnetic effects 査読

H Adachi, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 8 ) 2181 - 2184 2005年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Effects of Pauli paramagnetism on thermodynamic quantities in a vortex state, such as the specific heat C and magnetization M, are studied using the quasiclassical Eilenberger formalism. We demonstrate that with an increase of paramagnetic depairing effect, the sigh of the curvature of the field dependence of C changes from negative to positive, and that the Maki parameter kappa(2) becomes an increasing function of temperature. Our results provide a natural explanation for the unusual field dependence of C seen in CeCoIn5 in terms of the paramagnetic effect.

DOI： 10.1143/JPSJ.74.2181

Fulde-Ferrell-Larkin-Ovchinnikov states in a superfluid Fermi gas 査読

T Mizushima, M Ichioka, K Machida

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 ( 8-9 ) 1359 - 1361 2005年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Recently, both the experimental and theoretical studies to realize superfluid states in atomic gases have been performed by using a 50-50 mixture of atoms in two hyperfine spin states. We discuss favorable superfluid states in an unequal mixture. Such situation is analogous to a superconducting state in the presence of a magnetic field acting on the electron spins and then the natural candidate for the ground state is known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state which is a spatially inhomogeneous superfluid state. We examine the possibility of the FFLO state in two species gas of Fermions confined in a realistic three-dimensional harmonic trap. We propose a clear experimental way to create and directly detect the spatially modulated FFLO state from the macroscopic signature. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.05.067

Magnetization process in a chiral p-wave superconductor with multidomains 査読

M Ichioka, Y Matsunaga, K Machida

PHYSICAL REVIEW B 71 ( 17 ) 2005年5月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

A simulation study for the magnetization process is performed for the multidomain state in a chiral p-wave superconductor, using the time-dependent Ginzburg-Landau theory. The external field penetrates inside as cureless vortices through the domain wall, forming the vortex sheet structure. We find that, with increasing magnetic fields, the domain walls move so that the unstable domains shrink to vanish. Therefore, the single domain structure is realized at higher fields.

DOI： 10.1103/PhysRevB.71.172510

Double transition and vortex-sheet structure in multi-component superconductors 査読

M Ichioka, Y Matsunaga, K Machida

PHYSICA B-CONDENSED MATTER 359 539 - 541 2005年4月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

A simulation study using the time-dependent Ginzburg Landau theory is performed for the vortex state in two-component superconductors, in order to investigate the nature of the double transition and exotic vortex state, such as the vortex structure at the domain wall. Half flux-quantum vortices are aligned along the domain wall, forming vortex-sheet structure. The flux flow and the pinning of the vortex sheet are also investigated. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.140

Anisotropic diamagnetic response in type-II superconductors with gap and Fermi-surface anisotropies 査読

H Adachi, P Miranovic, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 94 ( 6 ) 2005年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The effects of anisotropic gap structures on a diamagnetic response are investigated in order to demonstrate that the field-angle-resolved magnetization [M-L (chi)] measurement can be used as a spectroscopic method to detect gap structures. Our microscopic calculation based on the quasiclassical Eilenberger formalism reveals that M-L (chi) in a superconductor with a fourfold gap displays a fourfold oscillation reflecting the gap and Fermi-surface anisotropies, and the sign of this oscillation changes at a field between H-c1 and H-c2. As a prototype of unconventional superconductors, magnetization data for borocarbides are also discussed.

DOI： 10.1103/PhysRevLett.94.067007

Direct imaging of spatially modulated superfluid phases in atomic fermion systems 査読

T Mizushima, K Machida, M Ichioka

PHYSICAL REVIEW LETTERS 94 ( 6 ) 2005年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

It is proposed that the spatially modulated superfluid phase, or the Fulde-Ferrell-Larkin-Ovchinnikov state could be observed in resonant fermion atomic condensates which are realized recently. We examine optimal experimental setups to achieve it by solving the Bogoliubov-de Gennes equation for both idealized one-dimensional and realistic three-dimensional cases. The spontaneous modulation of this superfluid is shown to be directly imaged as the density profiles either by optical absorption or by Stern-Gerlach experiments.

DOI： 10.1103/PhysRevLett.94.060404

Collective oscillations of vortices in Bose-Einstein condensates under rotation 査読

K. Machida, T. Mizushima, M. Ichioka

Laser Physics 15 ( 4 ) 660 - 668 2005年

Electronic state around vortex in a two-band superconductor 査読

Masanori Ichioka, Kazushige Machida, Noriyuki Nakai, Predrag Miranović

Physical Review B - Condensed Matter and Materials Physics 70 ( 14 ) 1 - 144508 2004年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Based on the quasiclassical theory, we investigate the vortex state in a two-band superconductor with a small gap on a three-dimensional Fermi surface and a large gap on a quasi-two dimensional one, as in MgB2. The field dependence of zero-energy density of states is compared for fields parallel and perpendicular to the ab plane, and the anisotropy of the vortex core shape is discussed for a parallel field. The Fermi surface geometry of two bands, combining the effect of the normal-like electronic state on the small gap band at high fields, produces characteristic behavior in the anisotropy of c and ab directions.

DOI： 10.1103/PhysRevB.70.144508

Flux flow and pinning of the vortex sheet structure in a two-component superconductor 査読

Yasushi Matsunaga, Masanori Ichioka, Kazushige Machida

Physical Review B - Condensed Matter and Materials Physics 70 ( 10 ) 1 - 100502 2004年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

A simulation study using the time-dependent Ginzburg-Landau theory is performed for the vortex state in two-component superconductors, such as PrOs4Sb12. We investigate the flux flow and the pinning of the vortex sheet structure. We find a domain wall that traps half flux-quantum vortices and moves with the flux flow. In the pinning case, we observe an emitting process of a conventional vortex from the vortex sheet by combining a pair of half flux-quantum vortices.

DOI： 10.1103/PhysRevB.70.100502

Field dependence of the zero-energy density of states around vortices in an anisotropic-gap superconductor 査読

N. Nakai, P. Miranović, M. Ichioka, K. Machida

Physical Review B - Condensed Matter and Materials Physics 70 ( 10 ) 1 - 100503 2004年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

It is shown theoretically that the Sommerfeld coefficient γ(B) in the mixed state contains useful information on the gap topology in a superconductor. We accurately evaluate γ(B) against magnetic induction B by using microscopic quasiclassical theory. The linear portion in γ(B) relative to 5c2 and its slope in low field faithfully corresponds to the gap anisotropy, so that we can distinguish the nodal gap and the anisotropic full gap, and estimate the magnitude of the gap anisotropy.

DOI： 10.1103/PhysRevB.70.100503

Effects of nonmagnetic scatterers on the local density of states around a vortex in s-wave superconductors 査読

P. Miranović, M. Ichioka, K. Machida

Physical Review B - Condensed Matter and Materials Physics 70 ( 10 ) 1 - 104510 2004年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We study the effect of nonmagnetic impurities on the local density of states (LDOS) in the mixed state of s-wave superconductors. The quasiclassical equations of superconductivity in the vortex state are solved self-consistently to show how the LDOS evolves with impurity concentration. The spatially averaged zero-energy LDOS is a linear function of magnetic induction in low fields, N(E=0)=α(τ)B/Hc2, for all impurity concentrations. The coefficient α depends weakly on the electron mean-free path. We evaluate numerically the differential conductance and spatial profiles of zero-energy LDOS, which can help in extracting the mean-free path from the measured LDOS.

DOI： 10.1103/PhysRevB.70.104510

Quasiparticle heat transport in mixed state of high-T-c superconductors 査読

M Takigawa, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 8 ) 2049 - 2052 2004年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The field dependence of low-temperature thermal conductivity kappa(H) observed on cuprates is explained by calculating kappa(H) microscopically. The heat current carried by low-lying quasiparticles around a vortex core decreases with H due to its depletion by the H-induced moment centered at a core for an underdoped case. This leads to a common and consistent picture on an "anomalous core". kappa(H, T) is found to be a useful tool for probing quasiparticle structures in the mixed state in general.

DOI： 10.1143/JPSJ.73.2049

Thermal conductivity of the vortex lattice state involving the antiferromagnetism around the core 査読

M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 404 ( 1-4 ) 375 - 379 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The thermal conductivity kappa(chichi) is the difference between higher and lower temperature regions, because the spatially-resolved thermal conductivity kappa(chichi)(r) is localized around the vortex core at lower temperature and delocalized at higher temperature. On one hand, much attention is focused on the spin and charge ordering around the vortex. When the antiferromagnetism appears around the core, the energy gap suppresses the density of states on the Fermi energy, and the zero-energy peak at the vortex core splits or vanishes. The kappa(chichi) under the Neel temperature is suppressed by the antiferromagnetism. We solve the Bogoliubov-de Gennes equation self-consistently by two-dimensional extended Hubbard model including the repulsive interaction U, and calculate the on the basis of the linear response theory. The picture of the spatial variation of the thermal conductivity kappa(r) through the spin resolved local DOS well explains recent experiments. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2003.09.091

Vortex state in double transition superconductors 査読

Y Matsunaga, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 92 ( 15 ) 2004年4月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The novel vortex phase and nature of the double transition field are investigated by two-component Ginzburg-Landau theory in a situation where fourfold-twofold symmetric superconducting double transition occurs. The deformation from 60degrees triangular vortex lattice and a possibility of the vortex sheet structure are discussed. In the presence of the gradient coupling, the transition changes to a crossover at finite field. These characters are important to identify the multiple superconducting phase in PrOs4Sb12.

DOI： 10.1103/PhysRevLett.92.157001

Expansion of vortex cores by strong electronic correlation in La2-xSrxCuO4 at low magnetic induction 査読

R Kadono, W Higemoto, A Koda, MI Larkin, GM Luke, AT Savici, YJ Uemura, KM Kojima, T Okamoto, T Kakeshita, S Uchida, T Ito, K Oka, M Takigawa, M Ichioka, K Machida

PHYSICAL REVIEW B 69 ( 10 ) 2004年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The vortex core radius rho(v), defined as the peak position of the supercurrent around the vortex, has been determined by muon spin rotation measurements in the mixed state of La2-xSrxCuO4 for x=0.13, 0.15, and 0.19. At lower doping (x=0.13 and 0.15), rho(v)(T) increases with decreasing temperature T, which is opposite to the behavior predicted by the conventional theory. Moreover, rho(v)(T-->0) is significantly larger than the Ginzburg-Landau coherence length determined by the upper critical field, and shows a clear tendency to decrease with increasing the doping x. These features can be qualitatively reproduced in a microscopic model involving antiferromagnetic electronic correlations.

DOI： 10.1103/PhysRevB.69.104523

Quasiparticle structure in antiferromagnetism around the vortex and nuclear magnetic relaxation time 査読

M Takigawa, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 2 ) 450 - 458 2004年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

On the basis of the Bogoliubov-de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure in d-wave superconductors is investigated including the contribution of the induced incommensurate antiferromagnetism around the vortex core. As the on-site repulsive interaction U increases, the spatial structure of charge and spin changes from the antiferromagnetic state with checkerboard modulation to that with the stripe modulation. By the effect of the induced antiferromagnetic moment, the zero-energy density of states is suppressed, and the vortex core radius increases. We also study the effect of the local density of states (LDOS) change on the site-dependent nuclear relaxation rate T-1(-1)(r). These results are compared with a variety of experiments performed on high T-c cuprates.

DOI： 10.1143/JPSJ.73.450

Beliaev damping of transverse quadrupole oscillations in single-vortex Bose-Einstein condensates 査読

T Mizushima, M Ichioka, K Machida, T Isoshima, MM Salomaa

LASER PHYSICS 14 ( 2 ) 295 - 301 2004年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：INTERPERIODICA

We investigate the damping mechanism of two transverse quadrupole oscillations in the single-vortex state of Bose-Einstein condensates using the linear response theory. It is demonstrated theoretically that the Kelvin modes as a propagation wave along a vortex line can be excited via Beliaev damping processes for only the counter-rotating quadrupole mode. We calculate the spectral weight of the density-response function within the Boooliubov-Popov theory in a cylindrical system taking into account both Beliaev and Landau processes. Furthermore, we extend these considerations to the full 3D cigar-shaped system, which enables us to discuss the effects of the longitudinal confinement on the damping processes. These results are compared with the recent experiment on Rb-87 by Bretin et al.

Fermi arc of metallic diagonal stripes in high-temperature superconducting cuprates 査読

E Kaneshita, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 10 ) 2441 - 2444 2003年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Spectral weight is investigated for the metallic diagonal stripe state in a two-dimensional Hubbard model, and the Fermi arc observed by the angle-resolved photoemission spectroscopy of La2-xSrxCuO4 is discussed. The Fermi arc coming from the midgap state of a diagonal stripe appears near (pi/2, pi/2) and at the equivalent positions in the reciprocal space, and the gap opens below the midgap state. We show how this spectral weight structure depends on the phasing of stripes, i.e., site- or bond-centered stripes.

DOI： 10.1143/JPSJ.72.2441

Excitation spectra of Bose-Einstein condensates in optical lattice 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 9 ) 2137 - 2140 2003年9月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The excitation spectra of Bose-Einstein condensates arc investigated in a three-dimensional optical lattice by the Bogoliubov theory considering the original sinusoidal potential for the optical lattice. When the lattice potential becomes high, the excitations show softening at large wavelengths, suggesting the breakdown of superfluidity. We also study the filling and interaction dependences of the properties of the excitation spectra and one-dimensional lattice case.

DOI： 10.1143/JPSJ.72.2137

Orientational field dependence of low-lying excitations in the mixed state of unconventional superconductors 査読

P Miranovic, N Nakai, M Ichioka, K Machida

PHYSICAL REVIEW B 68 ( 5 ) 2003年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

Orientational field dependence of the zero-energy density of states (ZEDOS) is calculated for superconductors with the polar state (line node), axial state (point node), and three-dimensional d-wave state. Depending on the gap topology and the relative field direction the field dependencies of ZEDOS sensitively differ, providing us a useful and practical method to identify the gap topology. It is also demonstrated that for d-wave state the field rotation in the basal plane shows a sizable oscillation (similar to3%) of ZEDOS. This is directly measurable in low-T specific heat experiment in the mixed state.

DOI： 10.1103/PhysRevB.68.052501

Dispersive gap mode of phonons in anisotropic superconductors 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 8 ) 2064 - 2070 2003年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the pairing function on the Fermi surface. When the sign of the pairing function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting pairing function.

DOI： 10.1143/JPSJ.72.2064

On superconducting double transition in PrOs4Sb12 査読

M Ichioka, N Nakai, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 6 ) 1322 - 1325 2003年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Superconducting double transition in PrOs4Sb12 is investigated by analyzing the anisotropy of the upper critical field H-c2 in the ab-plane, and the possible pairing state is discussed. When mixing due to gradient coupling is active, the twofold-symmetric component is necessarily induced in the fourfold symmetric phase, leading to the twofold oscillation of H-c2, contrary to the experimental result. To avoid the mixing effect, the weak spin-orbit coupling triplet pairing state is considered as a likely pairing function, where time-reversal symmetry is broken.

DOI： 10.1143/JPSJ.72.1322

Microscopic study of low-κ type-II superconductors 査読

P. Miranovic, N. Nakai, M. Ichioka, K. Machida

Physica B 329 1382 - 1383 2003年5月

Beliaev damping and Kelvin mode spectroscopy of a Bose-Einstein condensate in the presence of a vortex line 査読

T Mizushima, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 90 ( 18 ) 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

It is demonstrated theoretically that the counter-rotating quadrupole mode in a vortex of Bose-Einstein condensates can decay into a pair of Kelvin modes via the Beliaev process. We calculate the spectral weight of a density-response function within the Bogoliubov framework, taking account of both Beliaev and Landau processes. Good agreement with experiment on Rb-87 by Bretin et al. [Phys. Rev. Lett. 90, 100403 (2003)] allows us to unambigiously identify the decayed mode as the Kelvin wave propagating along a vortex line.

DOI： 10.1103/PhysRevLett.90.180401

Theoretical study on vortex lattices in tetragonal superconductors 査読

N Nakai, P Miranovic, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 677 - 678 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Vortex lattices of four fold symmetric superconductors are studied numerically on the basis of the quasiclassical theory. The four fold symmetric anisotropy of the Fermi velocity or the superconducting gap function causes the vortex lattice transformation. The transformation as observed in LuNi2B2C could be understood with the four fold symmetric anisotropy. We show the temperature and field phase diagram for four fold symmetric superconductors and the spatial structures of the pair potential and zero energy states in the case of the stable square vortex lattice at the low field. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02446-2

Field dependence of vortex structure in px±ipy-wave superconductors 査読

M. Ichioka, K. Shiroyama, K. Machida

Physica C 388 517 - 518 2003年5月

Multiple components of the order parameter induced around the d(x2)-(y2)-wave vortex core 査読

M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 667 - 668 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

On the basis of the Bogoliubov-de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure of d(x2-y2)-wave superconductors is analyzed. Multiple components of the order parameter are induced around the d(x2-y2)-wave vortex core. We study the spatial structure of the induced p(x) +/- ip(y) and extended s-wave components. We also study the case when the antiferromagnetism (checkerboard or stripe) is induced at the vortex core. There, spin-triplet d(x2-y2)-wave component is also induced. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02438-3

Study of phonon anomalies in stripe phase of high T-c cuprates 査読

E Kaneshita, M Ichioka, K Machida

PHYSICA B-CONDENSED MATTER 329 777 - 778 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We theoretically investigate phonon anomalies in various high T-c cuprates in terms of stripe concept. They could be caused by coupling with charge translational modes of stripes. The phonon self-energy correction is evaluated by taking into account the collective stripe modes. The coupling with stripes causes a phonon dispersion gap when the phonon dispersion has a steep slope around 2Q. No gap appears when the phonon spectrum has a flat dispersion around 2Q. Thus it turns out that these are depending on the slope of the phonon dispersions. (C) 2003 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4526(02)02527-9

Theoretical studies on vortices in unconventional and conventional superconductors 査読

K Machida, M Ichioka, P Miranovic, M Takigawa, N Nakai

ACTA PHYSICA POLONICA B 34 ( 2 ) 545 - 548 2003年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS

Vortex imaging method by the site selective NMR is explained by self-consistently solving the Bogoliubov-de Gennes equation for both s-wave and d-wave pairings. We analyze the temperature dependence of the relation time T-1 using the resonance frequency at the intensity maximum, namely the saddle point T-1 experiments. The site selective T-1 data are shown to yield valuable information on low-lying electronic excitations around a vortex core.

NMR relaxation time around a vortex in stripe superconductors 査読

M Takigawa, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 90 ( 4 ) 2003年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

Site-dependent NMR relaxation time T-1(r) is calculated in the vortex state using the Bogoliubov-de Gennes theory, taking account of possible "field-induced stripe" states in which the magnetism arises locally around a vortex core in d-wave superconductivity. The recently observed huge enhancement T-1(-1)(r) below T-c at a core site in Tl2Ba2CuO6 is explained. The field-induced stripe picture explains consistently other relevant STM and neutron experiments.

DOI： 10.1103/PhysRevLett.90.047001

Reentrant vortex lattice transformation in fourfold symmetric superconductors 査読

N Nakai, P Miranovic, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 89 ( 23 ) 2002年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The physics behind the rhombic-->square-->rhombic flux line lattice transformation in increasing fields is clarified on the basis of Eilenberger theory. We demonstrate that this reentrance observed in LuNi2B2C is due to intrinsic competition between the superconducting gap and Fermi surface anisotropies. The calculations not only reproduce it but also predict the not yet found lock-in transition to a square lattice with different orientation in a higher field. In view of the physical origin given, this sequence of transitions is rather generic to occur in fourfold symmetric superconductors.

DOI： 10.1103/PhysRevLett.89.237004

Superconducting gap modulation in weak stripe states 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 8 ) 1836 - 1839 2002年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The superconducting gap modulation is investigated in the presence of a weak stripe structure, using the Boooliubov-de Gennes theory on the two-dimensional Hubbard model with nearest-neighbor site pairing interaction. We calculate the local density of states and discuss the recently observed scanning tunneling spectroscopy data suggesting four-lattice periodicity on Bi2Sr2CaCu2O8+delta. We also consider the spectral weight in the reciprocal space, where the Fermi surface and the Superconducting gap are modulated by the band-folding effect of the stripe structure.

DOI： 10.1143/JPSJ.71.1836

Vortex structure in Sr2RuO4 査読

M Takigawa, M Ichioka, K Machida, M Sigrist

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1333 - 1336 2002年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

The vortex structure in p-wave superconductors is investigated by the Bogoliubov-de Gennes theory on a tight-binding model. We calculate the temperature dependence of the electronic state at each site in the vortex lattice state, and show the difference between sin p(x) + i sin p(y)-wave and sin p(x) - i sin p(y)-wave superconducting state. Furthermore the relation of the electronic structure and the site-dependence of the nuclear magnetic relaxation time is also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00086-0

Dynamical properties of stripes 査読

E Kaneshita, R Morino, M Ichioka, K Machida

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1545 - 1548 2002年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

The dynamical properties of stripes in high T-c oxide superconductors are studied theoretically at finite temperature (T) within RPA scheme on the two-dimensional Hubbard model. It is found that at lower dopings, the transverse dynamical susceptibility in the antiferromagnetic state exhibits the anomalous broadening of the spin wave spectral line width upon lowering T, indicating a phase transition to an incommensurate state. At a higher doping, the detailed T-evolutions of the spin wave spectrum are studied. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00074-4

Field dependence of the vortex structure in chiral p-wave superconductors 査読

M Ichioka, K Machida

PHYSICAL REVIEW B 65 ( 22 ) 2002年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

To investigate the different vortex structures between two chiral pairings p(x)+/-ip(y), we calculate the pair potential, the internal field, the local density of states, and the free energy in a vortex lattice state based on the quasiclassical Eilenberger theory, and analyze the magnetic-field dependence. The induced opposite chiral component of the pair potential plays an important role in the vortex structure. It also produces an rootH behavior of the zero-energy density of states at higher field. These results are helpful when we understand the vortex states in Sr2RuO4.

DOI： 10.1103/PhysRevB.65.224517

Phonon anomalies due to collective stripe modes in high T-c cuprates 査読

E Kaneshita, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 88 ( 11 ) 2002年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Phonon anomalies observed in various high T-c cuprates by neutron experiments are analyzed theoretically in terms of the stripe concept. The phonon self-energy correction is evaluated by taking into account the charge collective modes of stripes, giving rise to dispersion gap, or kink and shadow phonon modes at twice the wave number of spin stripe. These features coincide precisely with observations. The gapped branches of the phonon are found to be in-phase and out-of-phase oscillations relative to the charge collective mode.

DOI： 10.1103/PhysRevLett.88.115501

Vortex structure in P-wave superconductors based on tight-binding model 査読

N Nakai, M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 367 ( 1-4 ) 50 - 53 2002年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The spatial structure of the pair potential and the electronic state around a vortex is self-consistently calculated by the Bogoliubov-de Gennes theory on a tight-binding model with spin-triplet pairing interaction. We discuss the differences of the vortex structure for two chiral superconductivity of p(x) +/- ip(y)-wave, and the effects of the interband Cooper pair transfer on the vortex structure. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00989-3

Thermal conductivity in the vortex lattice of d-wave and s-wave superconductors 査読

M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 367 ( 1-4 ) 46 - 49 2002年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Thermal conductivity kappa(xx)(T) under a field is calculated by using a microscopic theory based on Bogoliubov-de Gennes equation for describing vortices and linear response theory. Superconductors with d(x2-y2)-wave and s-wave pairings are comparatively studied, modeled by a tight-binding extended Hubbard Hamiltonian in two spatial dimensions. The whole T-dependence of kappa(xx)(T) is calculated and shows the characteristic T-linear behavior in the lower T. This behavior is analyzed by examining the spatially resolved thermal flow patterns around a vortex. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00988-1

Vortex structure in chiral p-wave superconductors 査読

Masanori Ichioka, Kazushige Machida

Physical Review B - Condensed Matter and Materials Physics 65 ( 1 ) 145081 - 145089 2002年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

We investigate the vortex structure in chiral p-wave superconductors by the Bogoliubov-de Gennes theory on a tight-binding model. We calculate the spatial structure of the pair potential and electronic state around a vortex, including the anisotropy of the Fermi surface and superconducting gap structure. The differences of the vortex structure between sin px+i sin py-wave and sin px-i sin py-wave superconductors are clarified in the vortex lattice state. We also discuss the winding ∓3 case of the sin(px+py)±i sin(-px+py)-wave superconductivity.

DOI： 10.1103/PhysRevB.65.224517

Soliton excitations in halogen-bridged mixed-valence binuclear metal complexes 査読

S Yamamoto, M Ichioka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 1 ) 189 - 196 2002年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Motivated by recent stimulative observations in halogen (X)-bridged binuclear transition-metal (M) complexes, which are referred to as MMX chains, we study solitons in a one-dimensional three-quarter-filled charge-density-wave system with both intrasite and intersite electron-lattice couplings. Two distinct ground states of MMX chains are reproduced and the soliton excitations on them are compared. In the weak-coupling region, all the solitons are degenerate to each other and are uniquely scaled by the band gap, whereas in the strong-coupling region, they behave differently deviating from the scenario in the continuum limit. The soliton masses are calculated and compared with those for conventional mononuclear MX chains.

DOI： 10.1143/JPSJ.71.189

Field dependence of electronic specific heat in two-band superconductors 査読

N Nakai, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 1 ) 23 - 26 2002年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The vortex structure is studied in light of MgB2 theoretically based on a two-band superconducting model by means of Bogoliubov-de Gennes framework. The field dependence of the electronic specific heat coefficient gamma(H) is focused. The exponent alpha in gamma(H) alphaH(alpha) is shown to become smaller by adjusting the gap ratio of the two gaps on the major and minor bands. The observed extremely small value alpha similar to 0.23 could be reasonable in this two-band model with the gap ratio similar to0.3.

DOI： 10.1143/JPSJ.71.23

Vortex structure in chiral p-wave superconductors 査読

M Takigawa, M Ichioka, K Machida, M Sigrist

PHYSICAL REVIEW B 65 ( 1 ) 2002年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

We investigate the vortex structure in chiral p-wave superconductors by the Bogoliubov-de-Gennes theory on a tight-binding model. We calculate the spatial structure of the pair potential and electronic state around a vortex, including the anisotropy of the Fermi surface and superconducting gap structure, The differences of the vortex structure between sin p(x)+i sin p(y)-wave and sin p(x)-i sin p(y)-wave superconductors are clarified in the vortex lattice state. We also discuss the winding -/+3 case of the sin(p(x)+p(y))=i sin(-p(x)+p(y))-wave superconductivity.

DOI： 10.1103/PhysRevB.65.014508

Magnetic field dependence of the vortex structure based on the microscopic theory 査読

M Ichioka, M Takigawa, K Machida

VORTICES IN UNCONVENTIONAL SUPERCONDUCTORS AND SUPERFLUIDS 132 225 - 242 2002年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：SPRINGER-VERLAG BERLIN

We investigate the vortex structure in the vortex lattice state by the self-consistent numerical calculation based on the microscopic theory, and focus on the magnetic field dependence. First, we study the vortex structure Comparatively for the s-wave and the d(x2)-(y2)-wave pairing cases by the quasi-classical Eilenberger theory. We show the spatial variation of the local density of states (LDOS), and discuss the field dependence of the spatially averaged density of states, vortex core radius, and internal field distribution. Second, we propose the site-selective NMR relaxation time measurement as a new method to observe the quasiparticle state around the vortex core. We explain the relation between the LDOS and the temperature dependence, of the site-selective T-1 based on the Bogoliubov-de Gennes theory, and discuss the field dependence of the T-1-behavior.

Unconventional superconductivity with either multi-component or multi-band, or with chirality 査読

K Machida, M Ichioka, M Takigawa, N Nakai

RUTHENATE AND RUTHENO-CUPRATE MATERIALS 603 32 - 45 2002年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：SPRINGER-VERLAG BERLIN

In this review article, we discuss unconventional superconductivity where the unconventionality comes either from the multi-component order parameter, or from the multi-band order parameter, or from the chirality of the pairing function. These three typical form of unconventional superconductivity are analyzed in connection with materials such as UPt3 and UGe2 as the first example. MgB2 is mentioned as the second case where two distinctive energy gaps exist on different Fermi surface sheets. Sr2RuO4 is taken up as an example for chiral superconductivity. Here the vortex state in the mixed state in each superconductor is focused on from the view point of their unconventionality.

Relation between vortex excitation and thermal conductivity in superconductors

Masanori Ichioka

The European Physical Journal B 2002年

Collective modes of incommensurate spin density wave in one-dimensional Hubbard model 査読

M Ichioka, E Kaneshita, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 3 ) 818 - 828 2001年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Dynamical spin and charge susceptibility and collective modes are studied in the framework of the random phase approximation. They are calculated from the wave function of the selfconsistently obtained ground state, including all possible higher harmonics components of the ordering vector Q. We investigate a spin wave excitation in the spin transverse mode, and phason excitation related to the domain-wall motion in the spin longitudinal and charge modes. We consider the dispersion curve of the collective mode, and discuss the dependence on the on-site U interaction and the period of the incommensurate structure.

DOI： 10.1143/JPSJ.70.818

Spin and charge excitations in incommensurate spin density waves 査読

E Kaneshita, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 3 ) 866 - 876 2001年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Dynamical longitudinal spin susceptibility X-zz(q,w) and charge density susceptibility X-nn(q,w) are evaluated within random phase approximation for incommensurate spin density waves, or stripes, in two dimensional Hubbard model. Taking into account all possible higher harmonics of the fundamental component of the order parameter,we calculate these quantities for the full ranges of the momentum and energy, and analyze collective modes related to the motion of the stripe line. The anisotropy of the dispersion cone comes from the moving pattern of the stripes, i.e., the compression mode or the meandering mode. In the metallic stripe, there are also nesting excitations of the parallel sheet of the Fermi surfaces. We also discuss the excitation of the silent position in the insulating stripe.

DOI： 10.1143/JPSJ.70.866

Vortex structure in superconducting stripe states 査読

M Ichioka, M Takigawa, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 1 ) 33 - 36 2001年1月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The vortex structure in superconducting stripe states is studied according to the Bogoliubov-de Gennes theory on the two-dimensional Hubbard model with nearest-neighbor sites pairing interaction. The vortex is trapped at the outside region of the stripe line, where the superconductivity is weak. The superconducting coherence length along the stripe direction becomes long. There are no eminent low-energy electronic states even near the vortex core. These characters resemble the Josephson vortex in layered superconductors under a parallel field.

DOI： 10.1143/JPSJ.70.33

Static and Dynamical Properties of Stripes in Underdoped Cuprates 査読

Kazushige Machida, Masanori Ichioka, Eiji Kaneshita

Journal of the Physical Society of Japan, Suppl. A 2001年

Site-selective nuclear magnetic relaxation time in a superconducting vortex state 査読

M Takigawa, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 ( 12 ) 3943 - 3954 2000年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

On the basis of the microscopic Bogoliubov-de Gennes theory, the dependence of the nuclear spin relaxation time T-1 around vortices on the temperature and field is studied comparatively for both s-wave superconductor and d-wave superconductor. Reflecting low energy electronic excitations associated with the vortex core, the dependence of T-1 on the site and temperature deviate from those of the zero-field case, and T-1 becomes faster with approaching the vortex core. In the core region, T-1(-1) has a new peak below the superconducting transition temperature T-c. The dependence of the overall T-1(T) on the field for s-wave and d-wave superconductors is investigated and analyzed in terms of the local density of states. The NMR study by the dependence of T-1 on the resonance field may be a new method to probe the spatial resolved vortex core structure in various conventional and unconventional superconductors.

DOI： 10.1143/JPSJ.69.3943

Quasiparticle structure of stripes in high T-c cuprates 査読

M Ichioka, K Machida

PHYSICA B-CONDENSED MATTER 281 804 - 805 2000年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

We investigate the metallic stripe state by the self-consistent mean-field theory of the Hubbard model, focusing on La2-xSrxCuO4. We consider the band dispersion, the local density of states and the spectral weight to clarify the contribution of the mid-gap states. The superconducting state formed by quasiparticles of the stripe state is also studied. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)01025-X

Electronic structure of stripes in two-dimensional Hubbard model 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 ( 12 ) 4020 - 4031 1999年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Focusing on La2-xSrxCuO4, me study the stripe structure by the self-consistent mean-field theory of the Hubbard model. By introducing the realistic Fermi surface topology, the SDW-gapped insulator is changed to metallic. The solitonic features of the stripe structure and the contribution of the mid-gap states are presented. We consider the band dispersion, the local density of states, the spectral weight, and the optical conductivity, associated with the solitonic structure. These results may provide important information for the experimental research of the stripe structure, such as the angle-resolved photoemission experiments. The "Fermi surface" shape is changed depending on the ratio of the incommensurability delta and the hole density n(h). In real space, only the stripe region is metallic when delta/n(h) is large.

DOI： 10.1143/JPSJ.68.4020

Theory of vortex excitation imaging via an NMR relaxation measurement 査読

M Takigawa, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 83 ( 15 ) 3057 - 3060 1999年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The temperature dependence of the site-dependent nuclear spin relaxation time T-1 around vortices is studied in s-wave and d-wave superconductors. Reflecting low-energy electronic excitations associated with the vortex core, temperature dependences deviate from those of the zero-field case, and T-1 becomes faster when approaching the vortex core. In the core region, T-1(-1) has a new peak below T-c. The NMR study by the resonance field dependence may be a new method to prove the spatial resolved vortex core structure in various superconductors.

DOI： 10.1103/PhysRevLett.83.3057

Field dependence of the vortex structure in d-wave and s-wave superconductors 査読

M Ichioka, A Hasegawa, K Machida

JOURNAL OF SUPERCONDUCTIVITY 12 ( 4 ) 571 - 574 1999年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：KLUWER ACADEMIC/PLENUM PUBL

The vortex structure and its field dependence are studied in the clean limit on the basis of the quasi-classical Eilenberger theory to find their difference between d(x2-y2)- and s-wave pairings. We show the d(x2-y2)-wave nature and the vortex lattice effect on the local density of states around the vortex, and on the field dependence of the spatially averaged density of states. The d(x2-y2)-wave pairing introduces a fourfold symmetric structure around each vortex core in the pair potential and the internal held. With increasing field, their contribution becomes significant to the whole structure of the vortex lattice state.

DOI： 10.1023/A:1007752705983

Stripe structure, spectral feature and soliton gap in high T-c cuprates 査読

K Machida, M Ichioka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 ( 7 ) 2168 - 2171 1999年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOCIETY JAPAN

We show that lightly doped La2-xSrxCuO4 can be described in terms of a stripe magnetic structure or soliton picture. The internal relationship between the recent neutron observation of the diagonal (x=0.05) to vertical (x greater than or equal to 0.06) stripe transition, which was predicted, and the concomitant metal-insulator transition, is clarified by soliton physics. The phase diagram with the unidentified transition lines between the antiferromagnetic and stripe phases, the doping dependence of the modulation period, and the origin of the mid-infrared optical absorption are investigated and compared with other single-layer systems, La2-xSrxNiO4 and (La, Nd)(2-x)SrxCuO4. A novel type of quasi-particles and holes is fully responsible for metallic conduction and ultimately superconductivity.

DOI： 10.1143/JPSJ.68.2168

Field dependence of the vortex structure in d-wave and s-wave superconductors 査読

M Ichioka, A Hasegawa, K Machida

PHYSICAL REVIEW B 59 ( 13 ) 8902 - 8916 1999年4月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We study the vortex structure and its field dependence within the framework of the quasiclassical Eilenberger theory to find the difference between the d(x2-y2-) and s-wave pairings. We clarify the effect of the d(x2-y2)-wave nature and the vortex lattice effect on the vortex structure of the pair potential, the internal field and the local density of states. The d(x2-y2)-wave pairing introduces a fourfold-symmetric structure around each vortex core. With increasing field, their contribution becomes significant to the whole structure of the vortex lattice state, depending on the vortex lattice's configuration. It is reflected in the form factor of the internal field, which may be detected by small-angle neutron scattering, or the resonance line shape of muon spin resonance and NMR experiments. We also study the induced s- and d(xy)-wave components around the vortex in d(x2-y2)-wave superconductors. [S0163-1829(99)02213-4].

DOI： 10.1103/PhysRevB.59.8902

Vortex lattice effects on low-energy excitations in d-wave and s-wave superconductors 査読

M Ichioka, A Hasegawa, K Machida

PHYSICAL REVIEW B 59 ( 1 ) 184 - 187 1999年1月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Generic features of the low-energy excitations in the vortex lattice state are examined by comparatively studying the self-consistent solutions of the quasiclassical Eilenberger theory both for d(x2)-(y2)-wave and s-wave pairings. This low-energy physics associated with a vortex core, nodal structure, and quasiparticle transfer between vortices governs physical properties of the vortex such as the field dependences of the zero-energy density of states, the internal field distribution, and the shrinkage of the core radius. Eminent differences between two pairings an highlighted to help analyze experimental data. [S0163-1829(99)00102-2].

DOI： 10.1103/PhysRevB.59.184

Field dependence of the vortex structure in d-wave and s-wave superconductors 査読

Masanori Ichioka, Akiko Hasegawa, Kazushige Machida

Journal of Superconductivity and Novel Magnetism 12 ( 4 ) 571 - 574 1999年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The vortex structure and its field dependence are studied in the clean limit on the basis of the quasi-classical Eilenberger theory to find their difference between dx2-y2- and s-wave pairings. We show the dx2-y2-wave nature and the vortex lattice effect on the local density of states around the vortex, and on the field dependence of the spatially averaged density of states. The dx2-y2-wave pairing introduces a fourfold symmetric structure around each vortex core in the pair potential and the internal field. With increasing field, their contribution becomes significant to the whole structure of the vortex lattice state. © 1999 Plenum Publishing Corporation.

Relation between vortex core charge and vortex bound states 査読

N Hayashi, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 ( 10 ) 3368 - 3371 1998年10月

記述言語：英語出版者・発行元：PHYSICAL SOC JAPAN

Spatially inhomogeneous electron distribution around a single vortex is discussed on the basis of the Bogoliubov-de Gennes theory. The spatial structure and temperature dependence of the electron density around the vortex are presented. A relation between the vortex core charge and the vortex bound states (or the Caroli-de Gennes-Matricon states) is pointed out. Using the scanning tunneling microscope: information on the vortex core charge can he extracted through this relation.

DOI： 10.1143/JPSJ.67.3368

On the fourfold symmetry of H-c2 and magnetization of d(x(2)-y(2))-wave superconductors for the in-plane magnetic fields 査読

T Sugiyama, M Ichioka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 ( 5 ) 1738 - 1747 1998年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

For the d(x2-y2) superconductors, we investigate the foul-fold symmetry of the upper critical fields and magnetization related to the torque under the parallel magnetic field to the ab plane of the crystal. We take into account the s-wave order parameter induced from the spatial variation of the d(x2-y2)-wave order parameter. In addition, we investigate the effects of the shape of the Fermi surface. If the pairing interaction for the s-wave channel is attractive. the s-wave component can enhance the above fourfold symmetry. Depending on the structure of the Fermi surface, the fourfold symmetric anisotropy in the ab plane enhances or suppresses the fourfold symmetric behavior. There is also the case where the fourfold symmetric anisotropy of in the ab plane changes the sign of the fourfold symmetric behavior from that of the isotropic case.

DOI： 10.1143/JPSJ.67.1738

Low-lying quasiparticle excitations around a vortex core in quantum limit 査読

N Hayashi, T Isoshima, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 80 ( 13 ) 2921 - 2924 1998年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

Focusing on a quantum-limit behavior, we study a single vortex in a clean s-wave type-II superconductor by self-consistently solving the Bogoliubov-de Gennes equation. The discrete energy levels of the vortex bound states in the quantum limit are discussed. The vortex core radius shrinks monotonically up to an atomic-scale length on lowering the temperature T, and the shrinkage stops to saturate at a lower T. The pair potential, supercurrent, and local density of states around the vortex exhibit Friedel-like oscillations. The local density of states has particle-hole asymmetry induced by the vortex. These are potentially observed directly by scanning tunneling microscopy.

DOI： 10.1103/PhysRevLett.80.2921

Quasiparticle spectra around a single vortex in a d-wave superconductor - Comment 査読

M Franz, M Ichioka

PHYSICAL REVIEW LETTERS 79 ( 22 ) 4513 - 4513 1997年12月

Vortex lattice structure in a d(x(2)-y(2))-wave superconductor 査読

M Ichioka, N Enomoto, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 ( 12 ) 3928 - 3943 1997年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The vortex lattice structure in a d(x2-y2)-wave superconductor is investigated near the upper critical magnetic field in the framework of the Ginzburg Landau theory extended by including the correction terms such as the higher order derivatives derived from the Gor'kov equation. On lowering temperature, the unit cell shape of the vortex lattice gradually varies from a regular triangular lattice to a square lattice through the shape of an isosceles triangle. As for the orientation of the vortex lattice, the base of an isosceles triangle is along the a axis or the b axis of the crystal. The fourfold symmetric structure around a vortex core is also studied in the vortex lattice case. It is noted that these characteristic features appear even in the case the induced s-wave order parameter is absent around the vortex of the d(x2-y2)-wave superconductivity. We also investigate the effect of the induced s-wave order parameter. It enhances (suppresses) these characteristic features of the d(x2-y2)-wave superconductor when the s-wave component of the interaction is attractive (repulsive).

DOI： 10.1143/JPSJ.66.3928

Local density of states in the vortex lattice in a type-II superconductor 査読

M Ichioka, N Hayashi, K Machida

PHYSICAL REVIEW B 55 ( 10 ) 6565 - 6576 1997年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The local density of states (LDOS) in the triangular vortex lattice is investigated based on quasiclassical Eilenberger theory. We consider the case of an isotropic s-wave superconductor with the material parameter appropriate to NbSe2. At a weak magnetic field, the spatial Variation of the LDOS shows a cylindrical structure around a vortex core. On the other hand, at a high field where the core regions substantially overlap each other, the LDOS is a sixfold star-shaped structure due to the vortex lattice effect. The orientation of the star coincides with the experimental data of scanning tunneling microscopy. That is, the ray of the star extends toward the nearest-neighbor (next-nearest-neighbor) vortex direction at higher (lower) energy.

DOI： 10.1103/PhysRevB.55.6565

Ginzburg Landau theory for d-wave pairing and fourfold symmetric vortex core structure 査読

N Enomoto, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 ( 1 ) 204 - 214 1997年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

The Ginzburg Landau theory for d(x2-y2)-wave superconductors is constructed, by starting from the Gor'kov equation with including correction terms up to the next order of ln(T-c/T). Some of the non-local correction terms are found to break the cylindrical symmetry and lead to the fourfold symmetric core structure, reflecting the internal degree of freedom in the pair potential. Using this extended Ginzburg Landau theory, we investigate the fourfold symmetric structure of the pair potential, current and magnetic field around an isolated single vortex, and clarify concretely how the vortex core structure deviates from the cylindrical symmetry in the d(x2-y2)-wave superconductors.

DOI： 10.1143/JPSJ.66.204

Effects of gap anisotropy upon the electronic structure around a superconducting vortex 査読

Nobuhiko Hayashi, Masanori Ichioka, Kazushige Machida

Physical Review B - Condensed Matter and Materials Physics 56 ( 14 ) 9052 - 9063 1997年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

An isolated single vortex is considered within the framework of the quasiclassical theory. The local density of states around a vortex is calculated in a clean type-II superconductor with an anisotropy. The anisotropy of a superconducting energy gap is crucial for bound states around a vortex. A characteristic structure of the local density of states, observed in the layered hexagonal superconductor (Formula presented)-NbSe(Formula presented) by scanning tunneling microscopy (STM), is well reproduced if one assumes an anisotropic (Formula presented)-wave gap in the hexagonal plane. The local density of states (or the bound states) around the vortex is interpreted in terms of quasiparticle trajectories to facilitate an understanding of the rich electronic structure observed in STM experiments. It is pointed out that further fine structures and extra peaks in the local density of states should be observed by STM. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.56.9052

Star-shaped local density of states around vortices in a type-II superconductor 査読

N Hayashi, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 77 ( 19 ) 4074 - 4077 1996年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The electronic structure of vortices in a type II superconductor is analyzed within the quasiclassical Eilenberger framework. The possible origin of a sixfold ''star'' shape of the local density of states, observed by scanning tunneling microscope (STM) experiments on NbSe2, is examined in the light of the three effects: the anisotropic pairing, the vortex lattice, and the anisotropic density of states at the Fermi surface. Outstanding features of split parallel rays of this star are well explained in terms of an anisotropic s-wave pairing. This reveals not only a rich internal electronic structure associated with a vortex core, but also unique ability of the STM spectroscopy.

DOI： 10.1103/PhysRevLett.77.4074

Vortex structure in d-wave superconductors 査読

M Ichioka, N Hayashi, N Enomoto, K Machida

PHYSICAL REVIEW B 53 ( 22 ) 15316 - 15326 1996年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The vortex structure of pure d(x2-y2)-wave superconductors is microscopically analyzed in the framework of the quasiclassical Eilenberger equations. A self-consistent solution for the d-wave pair potential is obtained in the case of an isolated vortex. The vortex core structure, i.e., the pair potential, the supercurrent, and the magnetic field, is found to be fourfold symmetric even in the case that the mixing of the s-wave component is absent. The detailed temperature dependences of these quantities are calculated. The fourfold symmetry becomes clear when the temperature is decreased. The local density of states is calculated for the self-consistently obtained pair potential. From the results, we discuss the flow trajectory of the quasiparticles around a vortex, which is characteristic in d(x2-y2)-wave superconductors. The experimental relevance of our results to high-temperature superconductors is also given.

DOI： 10.1103/PhysRevB.53.15316

Vortex core structure and possible pairing mixture in d-wave superconductors 査読

K Machida, M Ichioka, N Hayashi, N Enomoto

PHYSICA C 263 ( 1-4 ) 428 - 430 1996年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The vortex core structure in a d-wave superconductor is analyzed by solving the quasi-classical Eilenberger equation self-consistently. The pair function, current and magnetic field distributions around an isolated vortex are found to break circular symmetry and show four-fold symmetry, reflecting the internal degrees of freedom in d-wave pairing.

DOI： 10.1016/0921-4534(95)00823-3

s- and d(xy)-wave components induced around a vortex in d(x(2)-y(2))-wave superconductors 査読

M Ichioka, N Enomoto, N Hayashi, K Machida

PHYSICAL REVIEW B 53 ( 5 ) 2233 - 2236 1996年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

The vortex structure of d(x2-y2)-wave superconductors is microscopically analyzed in the framework of the quasiclassical Eilenberger equations. If the pairing interaction contains an s-wave (d(xy)-wave) component in addition to a d(x2-y2)-wave component, the s-wave (d(xy)-wave) component of the order parameter is necessarily induced around a vortex in d(x2-y2)-wave superconductors. The spatial distribution of the induced s-wave and d(xy)-wave components is calculated. The s-wave component has an opposite winding number around the vortex near the d(x2-y2)-vortex core and its amplitude has the shape of a four-lobe clover. These are consistent with results based on the Ginzburg-Landau (GL) theory. The amplitude of the d(xy) component has the shape of an octofoil. The mixing of the d(xy) component cannot be explained by the GL theory, unless nonlocal correction terms are included.

DOI： 10.1103/PhysRevB.53.2233

VORTEX LATTICE OF LAYERED SUPERCONDUCTORS IN PARALLEL MAGNETIC-FIELDS 査読

M ICHIOKA

PHYSICAL REVIEW B 51 ( 14 ) 9423 - 9426 1995年4月

Fundamental Properties of a Vortex in a d-wave Superconductor (共著) 査読

ICHIOKA M, HAYASHI N, ENOMOTO N, MACHIDA K

Journal of the Physical Society of Japan 64 ( 12 ) 4547 - 4551 1995年

Collective Mode in Two-Band Superconductor : Condensed Matter and Statistical Physics 査読

Ichioka Masanori, Department of Physics Kyoto University

Progress of theoretical physics = Progress of theoretical physics 90 ( 3 ) 513 - 519 1993年9月

担当区分：筆頭著者記述言語：英語出版者・発行元：Published for the Research Institute for Fundamental Physics by Physical Society of Japan

Collective mode in two-band superconductor is investigated. The s-wave and d-wave modes in s-wave superconducting state are considered. We show the eigen-frequency of these modes as a function of temperature and the softening of the d-wave mode at the onset temperature of d-wave superconductivity.

DOI： 10.1143/PTP.90.513

その他リンク： https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=350956

SUPERCONDUCTIVITY IN 2-BAND MODEL

Masanori Ichioka

Progress of Theoretical Physics 1993年

　前のページ - 次のページ　

1