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

Yugova I. A. Gerlovin Ya. Davydov V. G. Ignatiev I. V. Kozin I. E. Ren H. W. Sugisaki M. Sugou S. Masumoto Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.66, no.23, pp.235312, 2002-12

被引用文献数

37 36

---

The paper reports on quantum beats observed in the photoluminescence kinetics of a single layer of the InPself-assembled quantum dots in a magnetic field. It is found that the beats arise only after removal of excesscharges from the quantum dots by an external electrical bias. The quantum beats are shown to be related to theinterference of the excitonic fine-structure states split by the magnetic-field. The dependences of the beatcharacteristics on the magnetic-field strength and orientation are studied. Theoretical analysis based on a modelspin Hamiltonian has allowed us to describe adequately the shape of the oscillating component of the signal.We have determined the values of the electron g-factor components and estimated the spread and the meanvalue of the hole g factor, as well as of the electron-hole exchange splitting parameters.

著者

Morishita M. Nagatani H.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.10, pp.104524, 2002-03

被引用文献数

15

---

Nuclear-spin heat capacities of submonolayer solid 3He adsorbed on a graphite surface are measured down to 100 μK, a factor of 20 lower temperature than in previous works. This system is one of the most ideal two-dimensional quantum spin systems (S=1/2). In a wide areal density region (6.1 nm-2<~ρ<~8.7 nm-2), anomalous temperature dependencies of the heat capacity, C∝Tα(-1.6≲α≲-0.7), are observed in a temperature range over two orders of magnitude (0.1 mK<~T<~20 mK) instead of the expected high-temperature behavior (α=-2) for localized spins. The α value shows a complicated density dependence which is accompanied by a density variation of a heat capacity isotherm at an extremely low temperature (=0.2 mK). This anomaly is similar to the previously observed high-temperature behavior (α≈-1) of the lowest density solid in the second layer. Although quantitative explanations are lacking for these anomalies, they are likely due to the high frustration caused by competing ferromagnetic and antiferromagnetic multiple-spin exchange interactions at least up to the six-spin exchange. We find that the excess heat-capacity (Cex) due to the amorphous 3He adsorbed on substrate heterogeneities is certainly not an origin of the anomalous behavior in C of the uniform submonolayer. Only at and below the density for the sqrt[3]×sqrt[3] commensurate phase (ρ=6.4 nm-2) heat capacity bumps at around 20 mK are observed. We suggest the possibility of spin-polaron effects caused by delocalized vacancies to explain this anomaly.

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

---

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

---

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

Aoki Sinya Fukaya Hidenori Hashimoto Shoji Onogi Tetsuya

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.76, no.5, pp.054508, 2007-09

被引用文献数

85 93

---

In finite volume the partition function of QCD with a given theta is a sum of different topological sectors with a weight primarily determined by the topological susceptibility. If a physical observable is evaluated only in a fixed topological sector, the result deviates from the true expectation value by an amount proportional to the inverse space-time volume 1/V. Using the saddle point expansion, we derive formulas to express the correction due to the fixed topological charge in terms of a 1/V expansion. Applying this formula, we propose a class of methods to determine the topological susceptibility in QCD from various correlation functions calculated in a fixed topological sector.

著者

Kojima Seiji Tsumura Naoki Wada Takeda Mitsuo Nishizawa Seizi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.67, no.3, pp.035102, 2003-01

被引用文献数

53 39

---

We report observations of the intensity and phase transmission spectra related to phonon-polariton propagation using coherent far-infrared radiation for a high-quality ferroelectric bismuth titanate crystal plate. In order to determine the polariton-dispersion relation, the phase delay was determined minutely as a function of the THz radiation frequency in the region between 3 and 100 cm-1. The anisotropy of polariton dispersion relation was also successfully determined on the c plate simply by switching the polarization direction of an incident beam from E∥a to E∥b. The observed polariton dispersion relations are consistently reproduced by the calculation using Kurosawa’s formula.

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

---

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

Hirai H. Tanaka T. Kawamura T. Yamamoto Y. Yagi T.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.68, no.17, pp.172102, 2003-11

被引用文献数

53 45

---

High-pressure experiments on methane hydrate were performed in the pressure range of 0.2–42 GPa using diamond-anvil cell. In situ x-ray-diffraction study revealed that methane hydrate of a high-pressure form, filled ice structure, survived up to 42 GPa. Pressure versus volume data were obtained in the pressure region. The filled ice structure represented large anisotropic compressibility and the volume change attained 40% at 42 GPa. The anisotropic compressibility was explained by the characteristic channel framework of the filled ice structure.

著者

Aoki S. Fukugita M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Ukawa A. Yamazaki T. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.9, pp.094504, 2005-05

被引用文献数

68

---

We calculate the two-pion wave function in the ground state of the I=2 S-wave system and find the interaction range between two pions, which allows us to examine the validity of the necessary condition for the finite-volume method for the scattering length proposed by Lüscher. We work in the quenched approximation employing a renormalization group improved gauge action for gluons and an improved Wilson action for quarks at 1/a=1.207(12) GeV on 163×80, 203×80, and 243×80 lattices. We conclude that the necessary condition is satisfied within the statistical errors for the lattice sizes L>=24 (3.92 fm) when the quark mass is in the range that corresponds to mpi2=0.273–0.736 GeV2. We obtain the scattering length with a smaller statistical error from the wave function than from the two-pion time correlator.

著者

Yamada N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Tsutsui N. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.5, pp.054505, 2005-03

被引用文献数

16 19

---

We perform a nonperturbative determination of the O(a)-improvement coefficient cSW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0–5.2 on a single lattice size of 83×16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for cSW and the critical hopping parameter Kc as a function of the bare coupling. This enables us to remove the O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for cSW suggests that finite volume effects in cSW are not large on the 83×16 lattice. We investigate Nf dependence of cSW by additional simulations for Nf=4, 2, and 0 at beta=9.6. As a preparatory step for this study, we also determine cSW in two-flavor QCD at beta=5.2. At this beta, several groups have carried out large-scale calculations of the hadron spectrum, while no systematic determination of cSW has been performed.

著者

Yamada N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Tsutsui N. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.5, pp.054505, 2005-03

被引用文献数

16 19

---

We perform a nonperturbative determination of the O(a)-improvement coefficient cSW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0–5.2 on a single lattice size of 83×16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for cSW and the critical hopping parameter Kc as a function of the bare coupling. This enables us to remove the O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for cSW suggests that finite volume effects in cSW are not large on the 83×16 lattice. We investigate Nf dependence of cSW by additional simulations for Nf=4, 2, and 0 at beta=9.6. As a preparatory step for this study, we also determine cSW in two-flavor QCD at beta=5.2. At this beta, several groups have carried out large-scale calculations of the hadron spectrum, while no systematic determination of cSW has been performed.

著者

Umeda T. Isoya J. Morishita N. Ohshima T. Kamiya T.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.69, pp.121201, 2004-03

被引用文献数

42

---

The EI5 and EI6 centers are typical intrinsic defects in radiation-damaged and semi-insulating 4H-SiC. So far, their origins have been assigned to positively charged carbon vacancies (VC+) and silicon antisites (SiC+), respectively. However, our complete set of 29Si hyperfine (HF) data clearly reveals that both the centers should originate from VC+ but their locations are different, i.e., quasicubic sites for EI5 and hexagonal sites for EI6, as recently predicted by the first-principle calculation [M. Bockstedte et al., Phys. Rev. B 67, 193102 (2003)]. The two types of VC+ centers showed remarkable differences in their atomic structures as well as in the temperature dependence of HF interactions, which are closely related to the nature of the two sites.

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

---

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

Morita Y. Hatsugai Y. Otsuka Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.70, no.24, pp.245101, 2004-12

被引用文献数

2 1

---

We study quasiparticle structure in the vicinity of the Heisenberg model. At first, we focus on the model in one dimension and show how solitonic quasiparticles (and their bound states) emerge. Further we discuss its anlaog in higher dimensions. Related to this subject, numerical data are presented and a discussion is given for the quasiparticles in the two-dimensional Hubbard model at half filling on a triangular-type lattice.

著者

Namekawa Y. Aoki S. Fukugita M. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. I. Okawa M. Ukawa A. Umeda T. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074503, 2004-10

被引用文献数

24 31

---

We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to mPS/mV=0.60–0.35. Numerical simulations are carried out using the RG-improved gauge action and the meanfield-improved clover quark action at beta=1.8 (a=0.2 fm from rho meson mass). We observe that the light hadron spectrum for small sea quark mass does not follow the expectation from chiral extrapolations with quadratic functions made from the region of mPS/mV=0.80–0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fail, the Wilson ChPT (WChPT) that includes a2 effects associated with explicit chiral symmetry breaking successfully fits the whole data: In particular, WChPT correctly predicts the light quark mass spectrum from simulations for medium heavy quark mass, such as mPS/mV>~0.5. Reanalyzing the previous data with the use of WChPT, we find the mean up and down quark mass being smaller than the previous result from quadratic chiral extrapolation by approximately 10%, mudMS-bar(µ=2 GeV)=3.11(17) [MeV] in the continuum limit.

著者

Yamazaki T. Aoki S. Fukugit M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074513, 2004-10

被引用文献数

82 94

---

We present a lattice QCD calculation of phase shift including the chiral and continuum extrapolations in two-flavor QCD. The calculation is carried out for I=2 S-wave pipi scattering. The phase shift is evaluated for two momentum systems, the center of mass and laboratory systems, by using the finite-volume method proposed by Lüscher in the center of mass system and its extension to general systems by Rummukainen and Gottlieb. The measurements are made at three different bare couplings beta=1.80, 1.95 and 2.10 using a renormalization group improved gauge and a tadpole improved clover fermion action, and employing a set of configurations generated for hadron spectroscopy in our previous work. The illustrative values we obtain for the phase shift in the continuum limit are delta(deg.)=-3.50(64), -9.5(30) and -16.9(64) for sqrt(s)(GeV)=0.4, 0.6 and 0.8, which are consistent with experiments.