研究者詳細 - 市岡　優典

論文 - 市岡　優典

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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

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