研究者詳細 - 市岡　優典

論文 - 市岡　優典

分割表示 188 件中 101 - 120 件目／全件表示 >>

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

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