研究者詳細 - 市岡　優典

論文 - 市岡　優典

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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

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