研究者詳細 - 市岡　優典

論文 - 市岡　優典

分割表示 188 件中 141 - 160 件目／全件表示 >>

Multiple components of the order parameter induced around the d(x2)-(y2)-wave vortex core 査読

M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 667 - 668 2003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：ELSEVIER SCIENCE BV

On the basis of the Bogoliubov-de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure of d(x2-y2)-wave superconductors is analyzed. Multiple components of the order parameter are induced around the d(x2-y2)-wave vortex core. We study the spatial structure of the induced p(x) +/- ip(y) and extended s-wave components. We also study the case when the antiferromagnetism (checkerboard or stripe) is induced at the vortex core. There, spin-triplet d(x2-y2)-wave component is also induced. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02438-3

Study of phonon anomalies in stripe phase of high T-c cuprates 査読

E Kaneshita, M Ichioka, K Machida

PHYSICA B-CONDENSED MATTER 329 777 - 778 2003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：ELSEVIER SCIENCE BV

We theoretically investigate phonon anomalies in various high T-c cuprates in terms of stripe concept. They could be caused by coupling with charge translational modes of stripes. The phonon self-energy correction is evaluated by taking into account the collective stripe modes. The coupling with stripes causes a phonon dispersion gap when the phonon dispersion has a steep slope around 2Q. No gap appears when the phonon spectrum has a flat dispersion around 2Q. Thus it turns out that these are depending on the slope of the phonon dispersions. (C) 2003 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4526(02)02527-9

Theoretical studies on vortices in unconventional and conventional superconductors 査読

K Machida, M Ichioka, P Miranovic, M Takigawa, N Nakai

ACTA PHYSICA POLONICA B 34 ( 2 ) 545 - 548 2003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：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS

Vortex imaging method by the site selective NMR is explained by self-consistently solving the Bogoliubov-de Gennes equation for both s-wave and d-wave pairings. We analyze the temperature dependence of the relation time T-1 using the resonance frequency at the intensity maximum, namely the saddle point T-1 experiments. The site selective T-1 data are shown to yield valuable information on low-lying electronic excitations around a vortex core.

NMR relaxation time around a vortex in stripe superconductors 査読

M Takigawa, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 90 ( 4 ) 2003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 SOC

Site-dependent NMR relaxation time T-1(r) is calculated in the vortex state using the Bogoliubov-de Gennes theory, taking account of possible "field-induced stripe" states in which the magnetism arises locally around a vortex core in d-wave superconductivity. The recently observed huge enhancement T-1(-1)(r) below T-c at a core site in Tl2Ba2CuO6 is explained. The field-induced stripe picture explains consistently other relevant STM and neutron experiments.

DOI： 10.1103/PhysRevLett.90.047001

Reentrant vortex lattice transformation in fourfold symmetric superconductors 査読

N Nakai, P Miranovic, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 89 ( 23 ) 2002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：AMERICAN PHYSICAL SOC

The physics behind the rhombic-->square-->rhombic flux line lattice transformation in increasing fields is clarified on the basis of Eilenberger theory. We demonstrate that this reentrance observed in LuNi2B2C is due to intrinsic competition between the superconducting gap and Fermi surface anisotropies. The calculations not only reproduce it but also predict the not yet found lock-in transition to a square lattice with different orientation in a higher field. In view of the physical origin given, this sequence of transitions is rather generic to occur in fourfold symmetric superconductors.

DOI： 10.1103/PhysRevLett.89.237004

Superconducting gap modulation in weak stripe states 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 8 ) 1836 - 1839 2002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：PHYSICAL SOC JAPAN

The superconducting gap modulation is investigated in the presence of a weak stripe structure, using the Boooliubov-de Gennes theory on the two-dimensional Hubbard model with nearest-neighbor site pairing interaction. We calculate the local density of states and discuss the recently observed scanning tunneling spectroscopy data suggesting four-lattice periodicity on Bi2Sr2CaCu2O8+delta. We also consider the spectral weight in the reciprocal space, where the Fermi surface and the Superconducting gap are modulated by the band-folding effect of the stripe structure.

DOI： 10.1143/JPSJ.71.1836

Vortex structure in Sr2RuO4 査読

M Takigawa, M Ichioka, K Machida, M Sigrist

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1333 - 1336 2002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：PERGAMON-ELSEVIER SCIENCE LTD

The vortex structure in p-wave superconductors is investigated by the Bogoliubov-de Gennes theory on a tight-binding model. We calculate the temperature dependence of the electronic state at each site in the vortex lattice state, and show the difference between sin p(x) + i sin p(y)-wave and sin p(x) - i sin p(y)-wave superconducting state. Furthermore the relation of the electronic structure and the site-dependence of the nuclear magnetic relaxation time is also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00086-0

Dynamical properties of stripes 査読

E Kaneshita, R Morino, M Ichioka, K Machida

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1545 - 1548 2002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：PERGAMON-ELSEVIER SCIENCE LTD

The dynamical properties of stripes in high T-c oxide superconductors are studied theoretically at finite temperature (T) within RPA scheme on the two-dimensional Hubbard model. It is found that at lower dopings, the transverse dynamical susceptibility in the antiferromagnetic state exhibits the anomalous broadening of the spin wave spectral line width upon lowering T, indicating a phase transition to an incommensurate state. At a higher doping, the detailed T-evolutions of the spin wave spectrum are studied. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00074-4

Field dependence of the vortex structure in chiral p-wave superconductors 査読

M Ichioka, K Machida

PHYSICAL REVIEW B 65 ( 22 ) 2002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：AMERICAN PHYSICAL SOC

To investigate the different vortex structures between two chiral pairings p(x)+/-ip(y), we calculate the pair potential, the internal field, the local density of states, and the free energy in a vortex lattice state based on the quasiclassical Eilenberger theory, and analyze the magnetic-field dependence. The induced opposite chiral component of the pair potential plays an important role in the vortex structure. It also produces an rootH behavior of the zero-energy density of states at higher field. These results are helpful when we understand the vortex states in Sr2RuO4.

DOI： 10.1103/PhysRevB.65.224517

Phonon anomalies due to collective stripe modes in high T-c cuprates 査読

E Kaneshita, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 88 ( 11 ) 2002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

Phonon anomalies observed in various high T-c cuprates by neutron experiments are analyzed theoretically in terms of the stripe concept. The phonon self-energy correction is evaluated by taking into account the charge collective modes of stripes, giving rise to dispersion gap, or kink and shadow phonon modes at twice the wave number of spin stripe. These features coincide precisely with observations. The gapped branches of the phonon are found to be in-phase and out-of-phase oscillations relative to the charge collective mode.

DOI： 10.1103/PhysRevLett.88.115501

Vortex structure in P-wave superconductors based on tight-binding model 査読

N Nakai, M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 367 ( 1-4 ) 50 - 53 2002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：ELSEVIER SCIENCE BV

The spatial structure of the pair potential and the electronic state around a vortex is self-consistently calculated by the Bogoliubov-de Gennes theory on a tight-binding model with spin-triplet pairing interaction. We discuss the differences of the vortex structure for two chiral superconductivity of p(x) +/- ip(y)-wave, and the effects of the interband Cooper pair transfer on the vortex structure. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00989-3

Thermal conductivity in the vortex lattice of d-wave and s-wave superconductors 査読

M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 367 ( 1-4 ) 46 - 49 2002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：ELSEVIER SCIENCE BV

Thermal conductivity kappa(xx)(T) under a field is calculated by using a microscopic theory based on Bogoliubov-de Gennes equation for describing vortices and linear response theory. Superconductors with d(x2-y2)-wave and s-wave pairings are comparatively studied, modeled by a tight-binding extended Hubbard Hamiltonian in two spatial dimensions. The whole T-dependence of kappa(xx)(T) is calculated and shows the characteristic T-linear behavior in the lower T. This behavior is analyzed by examining the spatially resolved thermal flow patterns around a vortex. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00988-1

Vortex structure in chiral p-wave superconductors 査読

Masanori Ichioka, Kazushige Machida

Physical Review B - Condensed Matter and Materials Physics 65 ( 1 ) 145081 - 145089 2002年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

We investigate the vortex structure in chiral p-wave superconductors by the Bogoliubov-de Gennes theory on a tight-binding model. We calculate the spatial structure of the pair potential and electronic state around a vortex, including the anisotropy of the Fermi surface and superconducting gap structure. The differences of the vortex structure between sin px+i sin py-wave and sin px-i sin py-wave superconductors are clarified in the vortex lattice state. We also discuss the winding ∓3 case of the sin(px+py)±i sin(-px+py)-wave superconductivity.

DOI： 10.1103/PhysRevB.65.224517

Soliton excitations in halogen-bridged mixed-valence binuclear metal complexes 査読

S Yamamoto, M Ichioka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 1 ) 189 - 196 2002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

Motivated by recent stimulative observations in halogen (X)-bridged binuclear transition-metal (M) complexes, which are referred to as MMX chains, we study solitons in a one-dimensional three-quarter-filled charge-density-wave system with both intrasite and intersite electron-lattice couplings. Two distinct ground states of MMX chains are reproduced and the soliton excitations on them are compared. In the weak-coupling region, all the solitons are degenerate to each other and are uniquely scaled by the band gap, whereas in the strong-coupling region, they behave differently deviating from the scenario in the continuum limit. The soliton masses are calculated and compared with those for conventional mononuclear MX chains.

DOI： 10.1143/JPSJ.71.189

Field dependence of electronic specific heat in two-band superconductors 査読

N Nakai, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 ( 1 ) 23 - 26 2002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 vortex structure is studied in light of MgB2 theoretically based on a two-band superconducting model by means of Bogoliubov-de Gennes framework. The field dependence of the electronic specific heat coefficient gamma(H) is focused. The exponent alpha in gamma(H) alphaH(alpha) is shown to become smaller by adjusting the gap ratio of the two gaps on the major and minor bands. The observed extremely small value alpha similar to 0.23 could be reasonable in this two-band model with the gap ratio similar to0.3.

DOI： 10.1143/JPSJ.71.23

Vortex structure in chiral p-wave superconductors 査読

M Takigawa, M Ichioka, K Machida, M Sigrist

PHYSICAL REVIEW B 65 ( 1 ) 2002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 SOC

We investigate the vortex structure in chiral p-wave superconductors by the Bogoliubov-de-Gennes theory on a tight-binding model. We calculate the spatial structure of the pair potential and electronic state around a vortex, including the anisotropy of the Fermi surface and superconducting gap structure, The differences of the vortex structure between sin p(x)+i sin p(y)-wave and sin p(x)-i sin p(y)-wave superconductors are clarified in the vortex lattice state. We also discuss the winding -/+3 case of the sin(p(x)+p(y))=i sin(-p(x)+p(y))-wave superconductivity.

DOI： 10.1103/PhysRevB.65.014508

Magnetic field dependence of the vortex structure based on the microscopic theory 査読

M Ichioka, M Takigawa, K Machida

VORTICES IN UNCONVENTIONAL SUPERCONDUCTORS AND SUPERFLUIDS 132 225 - 242 2002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：SPRINGER-VERLAG BERLIN

We investigate the vortex structure in the vortex lattice state by the self-consistent numerical calculation based on the microscopic theory, and focus on the magnetic field dependence. First, we study the vortex structure Comparatively for the s-wave and the d(x2)-(y2)-wave pairing cases by the quasi-classical Eilenberger theory. We show the spatial variation of the local density of states (LDOS), and discuss the field dependence of the spatially averaged density of states, vortex core radius, and internal field distribution. Second, we propose the site-selective NMR relaxation time measurement as a new method to observe the quasiparticle state around the vortex core. We explain the relation between the LDOS and the temperature dependence, of the site-selective T-1 based on the Bogoliubov-de Gennes theory, and discuss the field dependence of the T-1-behavior.

Unconventional superconductivity with either multi-component or multi-band, or with chirality 査読

K Machida, M Ichioka, M Takigawa, N Nakai

RUTHENATE AND RUTHENO-CUPRATE MATERIALS 603 32 - 45 2002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：SPRINGER-VERLAG BERLIN

In this review article, we discuss unconventional superconductivity where the unconventionality comes either from the multi-component order parameter, or from the multi-band order parameter, or from the chirality of the pairing function. These three typical form of unconventional superconductivity are analyzed in connection with materials such as UPt3 and UGe2 as the first example. MgB2 is mentioned as the second case where two distinctive energy gaps exist on different Fermi surface sheets. Sr2RuO4 is taken up as an example for chiral superconductivity. Here the vortex state in the mixed state in each superconductor is focused on from the view point of their unconventionality.

Relation between vortex excitation and thermal conductivity in superconductors

Masanori Ichioka

The European Physical Journal B 2002年

Collective modes of incommensurate spin density wave in one-dimensional Hubbard model 査読

M Ichioka, E Kaneshita, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 3 ) 818 - 828 2001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：PHYSICAL SOC JAPAN

Dynamical spin and charge susceptibility and collective modes are studied in the framework of the random phase approximation. They are calculated from the wave function of the selfconsistently obtained ground state, including all possible higher harmonics components of the ordering vector Q. We investigate a spin wave excitation in the spin transverse mode, and phason excitation related to the domain-wall motion in the spin longitudinal and charge modes. We consider the dispersion curve of the collective mode, and discuss the dependence on the on-site U interaction and the period of the incommensurate structure.

DOI： 10.1143/JPSJ.70.818

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