著者

Ishida Masahiko Takeuchi Osamu Mori Takehiko Shigekawa Hidemi

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.64, no.15, pp.153405, 2001-09

被引用文献数

9 10

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In addition to the intermolecular symmetry breaking which is generally observed during the surface relaxation/reconstruction of atomic crystals, intramolecular relaxation is expected to exist in the case of molecular crystals, which was confirmed on the surface of β-(BEDT-TTF)2PF6 [BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene] by using scanning tunneling microscopy (STM). Two types of molecular images obtained by STM were comprehensively explained by the spatial distributions of the highest-occupied molecular orbital calculated for the two types of the molecular structures. One is the structure appearing in the crystal that is derived from the x-ray diffraction measurement, which was used in the previous calculations to reproduce the STM images. The other is the relaxed molecular structure calculated by optimization of the molecular structure.

著者

Tomimoto S. Miyasaka S. Ogasawara T. Okamoto H. Tokura Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.68, no.3, pp.035106, 2003

被引用文献数

38 24

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The photoinduced effect on the orbital-ordered phase in perovskite-type LaVO3 has been investigated by femtosecond time-resolved reflection spectroscopy. Large reflectivity change has been observed immediately after photoirradiation. The spectral shape and polarization dependence of the reflectivity change indicate the melting of the orbital order induced by photoexcitation. The photocarriers annihilate in about 200 fs, and the orbital order partially recovers owing to thermalization with the lattice in 2–4 ps.

著者

Ryu Shinsei Hatsugai Yasuhiro

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.63, no.23, pp.233307, 2001-05

被引用文献数

9 9

---

The zero-mode wave function of a massless Dirac fermion in the presence of a random gauge field is studied. The density correlation function is calculated numerically, and found to exhibit a power law in the weak randomness with a disorder-dependent exponent. It deviates from the power law, and the disorder dependence becomes frozen in the strong randomness. A classical statistical system is employed through the replica trick to interpret the results, and the direct evaluation of the replica limit is demonstrated numerically. Analytical expressions of the correlation function and the free energy are also discussed with the replica symmetry breaking and the Liouville field theory.

著者

Ryu Shinsei Hatsugai Yasuhiro

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.65, no.3, pp.033301, 2001-12

被引用文献数

18

---

The Dirac fermion in the random chiral models is studied, which includes the random gauge field model and the random hopping model. We focus on a connection between continuum and lattice models to give a clear perspective for the random chiral models. Two distinct structures of density of states around zero energy, one is a power-law dependence on energy in the intermediate energy range and the other is a peak at zero energy, are revealed by an extensive numerical study for large systems up to 250×250. For the random hopping model, the above findings reconcile previous inconsistencies between the lattice and the continuum models.

著者

Tomimoto Shinichi Saito Shingo Suemoto Tohru Takeda Jun Kurita Susumu

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.66, no.15, pp.155112, 2002

被引用文献数

52

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The temporal evolution of the photoexcited state in quasi-one-dimensional (1D) halogen-bridged platinum complexes [Pt(en)2][Pt(en)2X2](ClO4)4 (abbreviated as Pt-X, X=Cl, Br or I), has been comprehensively studied by femtosecond time-resolved luminescence spectroscopy. In Pt-Cl, new short-lived hot luminescence is found in the low-energy side of a self-trapped exciton (STE) luminescence band. The overall behavior of the STE luminescence band within 2 ps is well explained by the vibrational relaxation of the STE. The behavior is reproduced by a model calculation based on wave packet propagation on an interaction mode composed of frequency-dispersed bulk phonons. This model is also applied to the previous results in Pt-Br. For both Pt-Cl and Pt-Br, the frequency spectra of phonons which compose the interaction mode have been estimated. In Pt-I, the STE luminescence decays much faster than those in Pt-Cl and Pt-Br, showing existence of more effective nonradiative decay channel.

著者

Otsuka Y. Hatsugai Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.65, no.7, pp.073101, 2002-01

被引用文献数

15

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Effects of the electron-electron interaction in the two-dimensional flux phase are investigated. We treat the half-filled Hubbard model with a magnetic flux π per plaquette by the quantum Monte Carlo method. When the interaction is small, an antiferromagnetic long-range order does not exist. It suggests that the Mott transition occurs at finite strength of the interaction in the flux phase, which is in contrast to the standard Hubbard model.

著者

Li Y. J. Takeuchi O. Futaba D. N. Oigawa H. Miyake K. Shigekawa H. Kuk Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.65, no.11, pp.113306, 2002-03

被引用文献数

3

---

Site-dependent adsorption structures of Xe atoms on a Si(111)-7×7 surface were studied by scanning tunneling microscopy at 8 K. Xe atoms initially adsorb as dimers on the site between a rest atom and its two neighboring center adatoms, and then near the corner adatom site. Similar structures were formed at both the faulted half (FH) and the unfaulted half (UH) of the 7×7 unit. The observed structure is in excellent agreement with that estimated by the rigid ball model, however, site-dependent bias dependence and different stabilities were observed for them, indicating the existence of different interactions between Xe and Si atoms in the 7×7 unit despite the stable electronic structure of Xe. Based on the results with thermal desorption spectroscopy, the adsorption energies are estimated to be 200 and 220 meV for FH and UH units, respectively.

著者

Hatsugai Y. Ryu S.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.65, no.21, pp.212510, 2002-06

被引用文献数

13 13

---

Topological quantum phase transitions in superconductivity are discussed on two-dimensional lattices. The main focus is on the Chern number for superconducting states. Each superconductivity is characterized by the Chern number, and the quantum phase transition is associated with topological changes of the quasiparticle Bloch function in the Brillouin zone. For the superconducting case, the Chern number has several equivalent but different topological expressions given by vortices, the Dirac monopole, and strings. We demonstrate quantum phase transitions by these topological quantities both for singlet and triplet cases.

著者

Brouwer P. W. Racine E. Furusaki A. Hatsugai Y. Morita Y. Mudry C.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.66, no.1, pp.014204, 2002-07

被引用文献数

32

---

If the number of lattice sites is odd, a quantum particle hopping on a bipartite lattice with random hopping between the two sublattices only is guaranteed to have an eigenstate at zero energy. We show that the localization length of this eigenstate depends strongly on the boundaries of the lattice, and can take values anywhere between the mean free path and infinity. The same dependence on boundary conditions is seen in the conductance of such a lattice if it is connected to electron reservoirs via narrow leads. For any nonzero energy, the dependence on boundary conditions is removed for sufficiently large system sizes.

著者

Otsuka Y. Morita Y. Hatsugai Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.66, no.7, pp.073109, 2002-08

被引用文献数

7

---

We investigate anisotropic charge fluctuations in the two-dimensional Hubbard model at half-filling. By the quantum Monte Carlo method, we calculate a momentum-resolved charge compressibility κ(k)=d〈n(k)〉/dμ, which shows the effects of an infinitesimal doping. At the temperature T∼t2/U, κ(k) shows a peak structure at the (±π/2,±π/2) points along the

著者

Sakai S. Tanimoto H. Kita E. Mizubayashi H.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.66, no.21, pp.214106, 2002-12

被引用文献数

16 17

---

Nanocrystalline (n) Au specimens with a density of 19.4±0.2 g/cm3 and a mean grain size of about 20 nm were prepared below 300 K by the gas deposition method, where two types of n-Au specimens were obtained as a function of a deposition rate, the type-H specimens above 800 nm/s and the type-L specimens below 800 nm/s. The anelastic and the plastic creep responses are similar qualitatively but different quantitatively between the type-H and type-L specimens. The anelastic strain ɛan,GB, associated with the grain boundary (GB) regions, increases linearly with (T-Tan1)(σap-σan1), when the temperature T is higher than a threshold temperature Tan1 of 200 K and the applied stress σap is higher than a threshold stress, σan1, of a few MPa. The ratio of ɛan,GB to the elastic strain is as large as 1.1 for the type-H specimens and 0.2 for the type-L specimens at 320 K for σap≫σan1. The activation energy for the GB anelastic process is 0.2 eV. We surmise that cooperative motions of many atoms in the GB regions are responsible for ɛan,GB, and both Tan1 and σan1 show a distribution depending on the number of atoms associated. The plastic creep rate ɛ′ vs σap data show a letter S-like curve. We classified the creep response into three categories, region I for the linear creep rate region for σap between σpc 1 and σpc2, region II for the transient creep rate region for σap between σpc2 and σpc3, and region III for the saturation creep rate region for σap between σpc3 and σy. The threshold stresses σpc1 and σpc2 and the yield stress σy are about 30, 150, and 360 MPa for the type-H specimens, and about 60, 300, and 500 MPa for the type-L specimens, respectively. σpc3 is slightly lower than σy. From scanning tunneling microscopy images, we surmise that the localized GB slip takes place in region I, and the mean separation between the localized GB slips decreases with increasing σap in region II and becomes comparable with the mean grain size in region III. The plastic creep in region III may be explained by the Ashby creep. The present view for the creep behavior explains the low-temperature creep behavior of fcc n metals.

著者

Mirković J. Savel’ev S. E. Sugahara E. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.66, no.13, pp.132505, 2002-10

被引用文献数

13 12

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The vortex-liquid and vortex-solid phases in single crystals of Bi2Sr2CaCu2O8+δ placed in tilted magnetic fields are studied by in-plane resistivity measurements using the Corbino geometry to avoid spurious surface-barrier effects. It was found that the anisotropy of the vortex-solid phase increases with temperature and exhibits a maximum at T≈0.97Tc. In contrast, the anisotropy of the vortex-liquid phase rises monotonically across the whole measured temperature range. The observed behavior is discussed in the context of dimensional crossover and thermal fluctuations of vortices in the strongly layered system.

著者

Kawano-Furukawa H. Yoshizawa H. Takeya H. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.66, no.21, pp.212503, 2002-12

被引用文献数

6 7

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An anomalous phonon peak that appears only in the superconducting state has been reported for nonmagnetic intermetallic superconductor RNi211B2C (R=Y, Lu). In the present paper, we shall demonstrate that another rare-earth borocarbide ErNi211B2C seems to show similar phonon anomalies. A spectral weight transfer from the above-lying TA phonon mode to the aforementioned peak was rather small, but it is consistent with the theoretical prediction for the system with smaller 2Δ/Eph ratio. Combining the present results with those observed in the other borocarbide systems, we suggest that such a phonon anomaly might be a common phenomenon for superconductors with a strong nesting feature of the Fermi surface.

著者

Machida Y. Sasaki S. Fujii H. Furuyama M. Kakeya I. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.67, no.9, pp.094507, 2003-03

被引用文献数

31 37

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We synthesized single crystalline MgB2 under ambient pressure by using conventional materials and equipment. The single crystals of MgB2 were of good quality, where the crystal structure refinements were successfully converged with R=0.020. The measurements of the magnetic properties yielded a sharp superconducting transition at 38 K with transition width ΔTc=0.8 K. The upper critical field for applied field parallel to the ab plane (Hc2ab) reveals a positive curvature, while Hc2 parallel to the c axis (Hc2c) increases linearly in temperature dependence, which yields a temperature dependence of the superconducting anisotropy ratio of γ=Hc2ab/Hc2c with γ∼1 near Tc and 4.0 at 25 K.

著者

Kaminski A. Rosenkranz S. Fretwell H. M. Mesot J. Randeria M. Campuzano J. C. Norman M. R. Li Z. Z. Raffy H. Sato T. Takahashi T. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.69, pp.212509, 2004-06

被引用文献数

31 34

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One of the interesting features of the photoemission spectra of the high temperature cuprate superconductors is the presence of a large signal (referred to as the "background") in the unoccupied region of the Brillouin zone. Here we present data indicating that the background signal is a component of the photocurrent that is separate from the spectral function and is most likely due to strong scattering of the photoelectrons. We also present an analytical method that can be used to subtract the background signal.

著者

Shimada Kenya Mizokawa Takashi Mamiya Kazutoshi Saitoh Tomohiko Fujimori Atsushi Ono Kanta Kakizaki Akito Ishii Takehiko Shirai Masafumi Kamimura Takashi

出版者

American Physical Society

雑誌

Physical Review B - Condensed Matter and Materials Physics (ISSN:01631829)

巻号頁・発行日

vol.57, no.15, pp.8845-8853, 1998-04-15

被引用文献数

3 43

---

The electronic structures of the antiferromagnetic semiconductor FeS and ferrimagnetic metals Fe7S8 and Fe7Se8 have been studied by spin-integrated and spin-resolved photoemission spectroscopy and inverse-photoemission spectroscopy. The overall Fe 3d bandwidth in the photoemission spectra is 25-30 % narrower than the density of states (DOS) predicted by first-principles band-structure calculations and is accompanied by an intense tail on the high-binding-energy side, indicating the correlated nature of electrons in the Fe 3d band. Deviation from the band DOS is more significant in Fe7S8 than in Fe7Se8, and in the minority-spin spectra than in the majority-spin spectra. Cluster-model calculation for FeS has shown satellite structures at high binding energies, but the calculated spectral line shape is not in good agreement with experiment compared to the band DOS. By introducing a self-energy correction to the band DOS, we could explain the narrowing of the overall Fe 3d bandwidth and the high-binding-energy tail shape but not for the unusual broadening of the Fe 3d band within ∼ 1 eV of the Fermi level.

著者

Kawamoto Tadashi Mori Takehiko Takimiya Kazuo Kataoka Yoshiro Aso Yoshio Otsubo Tetsuo

出版者

American Physical Society

雑誌

Physical Review B - Condensed Matter and Materials Physics (ISSN:01631829)

巻号頁・発行日

vol.65, no.14, pp.140508-1-140508-4, 2002-03-28

被引用文献数

7 42

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The degree of charge transfer and the upper critical field of the organic superconductor (MDT-TSF)(AuI2)x have been investigated (MDT-TSF: methylenedithio-tetraselenafulvalene). The x-ray oscillation photograph indicates that the anion lattice is incommensurate with the donor lattice, and the chemical composition is (MDT-TSF)(AuI2)0.44 . The charge-transfer degree of this salt is 0.44. The electrical resistivity and the Seebeck coefficient indicate that this salt is a good Fermi liquid above the superconducting transition temperature. The upper critical fields show anisotropic three-dimensional character in spite of the complicated incommensurate structure, and are within the Clogston-Chandrasekhar paramagnetic limit in all directions.