研究者詳細 - 市岡　優典

論文 - 市岡　優典

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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

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