研究者詳細 - 市岡　優典

論文 - 市岡　優典

分割表示 188 件中 121 - 140 件目／全件表示 >>

Collective oscillations of vortices in Bose-Einstein condensates under rotation 査読

K. Machida, T. Mizushima, M. Ichioka

Laser Physics 15 ( 4 ) 660 - 668 2005年

Electronic state around vortex in a two-band superconductor 査読

Masanori Ichioka, Kazushige Machida, Noriyuki Nakai, Predrag Miranović

Physical Review B - Condensed Matter and Materials Physics 70 ( 14 ) 1 - 144508 2004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

Based on the quasiclassical theory, we investigate the vortex state in a two-band superconductor with a small gap on a three-dimensional Fermi surface and a large gap on a quasi-two dimensional one, as in MgB2. The field dependence of zero-energy density of states is compared for fields parallel and perpendicular to the ab plane, and the anisotropy of the vortex core shape is discussed for a parallel field. The Fermi surface geometry of two bands, combining the effect of the normal-like electronic state on the small gap band at high fields, produces characteristic behavior in the anisotropy of c and ab directions.

DOI： 10.1103/PhysRevB.70.144508

Flux flow and pinning of the vortex sheet structure in a two-component superconductor 査読

Yasushi Matsunaga, Masanori Ichioka, Kazushige Machida

Physical Review B - Condensed Matter and Materials Physics 70 ( 10 ) 1 - 100502 2004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 simulation study using the time-dependent Ginzburg-Landau theory is performed for the vortex state in two-component superconductors, such as PrOs4Sb12. We investigate the flux flow and the pinning of the vortex sheet structure. We find a domain wall that traps half flux-quantum vortices and moves with the flux flow. In the pinning case, we observe an emitting process of a conventional vortex from the vortex sheet by combining a pair of half flux-quantum vortices.

DOI： 10.1103/PhysRevB.70.100502

Field dependence of the zero-energy density of states around vortices in an anisotropic-gap superconductor 査読

N. Nakai, P. Miranović, M. Ichioka, K. Machida

Physical Review B - Condensed Matter and Materials Physics 70 ( 10 ) 1 - 100503 2004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 theoretically that the Sommerfeld coefficient γ(B) in the mixed state contains useful information on the gap topology in a superconductor. We accurately evaluate γ(B) against magnetic induction B by using microscopic quasiclassical theory. The linear portion in γ(B) relative to 5c2 and its slope in low field faithfully corresponds to the gap anisotropy, so that we can distinguish the nodal gap and the anisotropic full gap, and estimate the magnitude of the gap anisotropy.

DOI： 10.1103/PhysRevB.70.100503

Effects of nonmagnetic scatterers on the local density of states around a vortex in s-wave superconductors 査読

P. Miranović, M. Ichioka, K. Machida

Physical Review B - Condensed Matter and Materials Physics 70 ( 10 ) 1 - 104510 2004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 study the effect of nonmagnetic impurities on the local density of states (LDOS) in the mixed state of s-wave superconductors. The quasiclassical equations of superconductivity in the vortex state are solved self-consistently to show how the LDOS evolves with impurity concentration. The spatially averaged zero-energy LDOS is a linear function of magnetic induction in low fields, N(E=0)=α(τ)B/Hc2, for all impurity concentrations. The coefficient α depends weakly on the electron mean-free path. We evaluate numerically the differential conductance and spatial profiles of zero-energy LDOS, which can help in extracting the mean-free path from the measured LDOS.

DOI： 10.1103/PhysRevB.70.104510

Quasiparticle heat transport in mixed state of high-T-c superconductors 査読

M Takigawa, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 8 ) 2049 - 2052 2004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

The field dependence of low-temperature thermal conductivity kappa(H) observed on cuprates is explained by calculating kappa(H) microscopically. The heat current carried by low-lying quasiparticles around a vortex core decreases with H due to its depletion by the H-induced moment centered at a core for an underdoped case. This leads to a common and consistent picture on an "anomalous core". kappa(H, T) is found to be a useful tool for probing quasiparticle structures in the mixed state in general.

DOI： 10.1143/JPSJ.73.2049

Thermal conductivity of the vortex lattice state involving the antiferromagnetism around the core 査読

M Takigawa, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 404 ( 1-4 ) 375 - 379 2004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

The thermal conductivity kappa(chichi) is the difference between higher and lower temperature regions, because the spatially-resolved thermal conductivity kappa(chichi)(r) is localized around the vortex core at lower temperature and delocalized at higher temperature. On one hand, much attention is focused on the spin and charge ordering around the vortex. When the antiferromagnetism appears around the core, the energy gap suppresses the density of states on the Fermi energy, and the zero-energy peak at the vortex core splits or vanishes. The kappa(chichi) under the Neel temperature is suppressed by the antiferromagnetism. We solve the Bogoliubov-de Gennes equation self-consistently by two-dimensional extended Hubbard model including the repulsive interaction U, and calculate the on the basis of the linear response theory. The picture of the spatial variation of the thermal conductivity kappa(r) through the spin resolved local DOS well explains recent experiments. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2003.09.091

Vortex state in double transition superconductors 査読

Y Matsunaga, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 92 ( 15 ) 2004年4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

The novel vortex phase and nature of the double transition field are investigated by two-component Ginzburg-Landau theory in a situation where fourfold-twofold symmetric superconducting double transition occurs. The deformation from 60degrees triangular vortex lattice and a possibility of the vortex sheet structure are discussed. In the presence of the gradient coupling, the transition changes to a crossover at finite field. These characters are important to identify the multiple superconducting phase in PrOs4Sb12.

DOI： 10.1103/PhysRevLett.92.157001

Expansion of vortex cores by strong electronic correlation in La2-xSrxCuO4 at low magnetic induction 査読

R Kadono, W Higemoto, A Koda, MI Larkin, GM Luke, AT Savici, YJ Uemura, KM Kojima, T Okamoto, T Kakeshita, S Uchida, T Ito, K Oka, M Takigawa, M Ichioka, K Machida

PHYSICAL REVIEW B 69 ( 10 ) 2004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

The vortex core radius rho(v), defined as the peak position of the supercurrent around the vortex, has been determined by muon spin rotation measurements in the mixed state of La2-xSrxCuO4 for x=0.13, 0.15, and 0.19. At lower doping (x=0.13 and 0.15), rho(v)(T) increases with decreasing temperature T, which is opposite to the behavior predicted by the conventional theory. Moreover, rho(v)(T-->0) is significantly larger than the Ginzburg-Landau coherence length determined by the upper critical field, and shows a clear tendency to decrease with increasing the doping x. These features can be qualitatively reproduced in a microscopic model involving antiferromagnetic electronic correlations.

DOI： 10.1103/PhysRevB.69.104523

Quasiparticle structure in antiferromagnetism around the vortex and nuclear magnetic relaxation time 査読

M Takigawa, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 2 ) 450 - 458 2004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：PHYSICAL SOC JAPAN

On the basis of the Bogoliubov-de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure in d-wave superconductors is investigated including the contribution of the induced incommensurate antiferromagnetism around the vortex core. As the on-site repulsive interaction U increases, the spatial structure of charge and spin changes from the antiferromagnetic state with checkerboard modulation to that with the stripe modulation. By the effect of the induced antiferromagnetic moment, the zero-energy density of states is suppressed, and the vortex core radius increases. We also study the effect of the local density of states (LDOS) change on the site-dependent nuclear relaxation rate T-1(-1)(r). These results are compared with a variety of experiments performed on high T-c cuprates.

DOI： 10.1143/JPSJ.73.450

Beliaev damping of transverse quadrupole oscillations in single-vortex Bose-Einstein condensates 査読

T Mizushima, M Ichioka, K Machida, T Isoshima, MM Salomaa

LASER PHYSICS 14 ( 2 ) 295 - 301 2004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：INTERPERIODICA

We investigate the damping mechanism of two transverse quadrupole oscillations in the single-vortex state of Bose-Einstein condensates using the linear response theory. It is demonstrated theoretically that the Kelvin modes as a propagation wave along a vortex line can be excited via Beliaev damping processes for only the counter-rotating quadrupole mode. We calculate the spectral weight of the density-response function within the Boooliubov-Popov theory in a cylindrical system taking into account both Beliaev and Landau processes. Furthermore, we extend these considerations to the full 3D cigar-shaped system, which enables us to discuss the effects of the longitudinal confinement on the damping processes. These results are compared with the recent experiment on Rb-87 by Bretin et al.

Fermi arc of metallic diagonal stripes in high-temperature superconducting cuprates 査読

E Kaneshita, M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 10 ) 2441 - 2444 2003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

Spectral weight is investigated for the metallic diagonal stripe state in a two-dimensional Hubbard model, and the Fermi arc observed by the angle-resolved photoemission spectroscopy of La2-xSrxCuO4 is discussed. The Fermi arc coming from the midgap state of a diagonal stripe appears near (pi/2, pi/2) and at the equivalent positions in the reciprocal space, and the gap opens below the midgap state. We show how this spectral weight structure depends on the phasing of stripes, i.e., site- or bond-centered stripes.

DOI： 10.1143/JPSJ.72.2441

Excitation spectra of Bose-Einstein condensates in optical lattice 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 9 ) 2137 - 2140 2003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：PHYSICAL SOC JAPAN

The excitation spectra of Bose-Einstein condensates arc investigated in a three-dimensional optical lattice by the Bogoliubov theory considering the original sinusoidal potential for the optical lattice. When the lattice potential becomes high, the excitations show softening at large wavelengths, suggesting the breakdown of superfluidity. We also study the filling and interaction dependences of the properties of the excitation spectra and one-dimensional lattice case.

DOI： 10.1143/JPSJ.72.2137

Orientational field dependence of low-lying excitations in the mixed state of unconventional superconductors 査読

P Miranovic, N Nakai, M Ichioka, K Machida

PHYSICAL REVIEW B 68 ( 5 ) 2003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：AMERICAN PHYSICAL SOC

Orientational field dependence of the zero-energy density of states (ZEDOS) is calculated for superconductors with the polar state (line node), axial state (point node), and three-dimensional d-wave state. Depending on the gap topology and the relative field direction the field dependencies of ZEDOS sensitively differ, providing us a useful and practical method to identify the gap topology. It is also demonstrated that for d-wave state the field rotation in the basal plane shows a sizable oscillation (similar to3%) of ZEDOS. This is directly measurable in low-T specific heat experiment in the mixed state.

DOI： 10.1103/PhysRevB.68.052501

Dispersive gap mode of phonons in anisotropic superconductors 査読

M Ichioka, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 8 ) 2064 - 2070 2003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

We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the pairing function on the Fermi surface. When the sign of the pairing function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting pairing function.

DOI： 10.1143/JPSJ.72.2064

On superconducting double transition in PrOs4Sb12 査読

M Ichioka, N Nakai, K Machida

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 ( 6 ) 1322 - 1325 2003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：PHYSICAL SOC JAPAN

Superconducting double transition in PrOs4Sb12 is investigated by analyzing the anisotropy of the upper critical field H-c2 in the ab-plane, and the possible pairing state is discussed. When mixing due to gradient coupling is active, the twofold-symmetric component is necessarily induced in the fourfold symmetric phase, leading to the twofold oscillation of H-c2, contrary to the experimental result. To avoid the mixing effect, the weak spin-orbit coupling triplet pairing state is considered as a likely pairing function, where time-reversal symmetry is broken.

DOI： 10.1143/JPSJ.72.1322

Microscopic study of low-κ type-II superconductors 査読

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

Physica B 329 1382 - 1383 2003年5月

Beliaev damping and Kelvin mode spectroscopy of a Bose-Einstein condensate in the presence of a vortex line 査読

T Mizushima, M Ichioka, K Machida

PHYSICAL REVIEW LETTERS 90 ( 18 ) 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：AMERICAN PHYSICAL SOC

It is demonstrated theoretically that the counter-rotating quadrupole mode in a vortex of Bose-Einstein condensates can decay into a pair of Kelvin modes via the Beliaev process. We calculate the spectral weight of a density-response function within the Bogoliubov framework, taking account of both Beliaev and Landau processes. Good agreement with experiment on Rb-87 by Bretin et al. [Phys. Rev. Lett. 90, 100403 (2003)] allows us to unambigiously identify the decayed mode as the Kelvin wave propagating along a vortex line.

DOI： 10.1103/PhysRevLett.90.180401

Theoretical study on vortex lattices in tetragonal superconductors 査読

N Nakai, P Miranovic, M Ichioka, K Machida

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 677 - 678 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

Vortex lattices of four fold symmetric superconductors are studied numerically on the basis of the quasiclassical theory. The four fold symmetric anisotropy of the Fermi velocity or the superconducting gap function causes the vortex lattice transformation. The transformation as observed in LuNi2B2C could be understood with the four fold symmetric anisotropy. We show the temperature and field phase diagram for four fold symmetric superconductors and the spatial structures of the pair potential and zero energy states in the case of the stable square vortex lattice at the low field. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02446-2

Field dependence of vortex structure in px±ipy-wave superconductors 査読

M. Ichioka, K. Shiroyama, K. Machida

Physica C 388 517 - 518 2003年5月

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