研究者詳細 - 市岡　優典

論文 - 市岡　優典

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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

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