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

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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

Kozin I. E. Davydov V. G. Ignatiev I. V. Kavokin A. V. Kavokin K. V. Malpuech G. Ren Hong-Wen 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.65, no.24, pp.241312, 2002-06

被引用文献数

61 53

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Spins of resident electrons in charged quantum dots (QD’s) act as local magnets inducing the Zeeman splitting of excitons trapped into dots. This is evidenced by the observation of quantum beats in the linearly polarized time-resolved photoluminescence of a biased array of self-assembled InP QD’s. An external magnetic field is found to shorten the spin beats’ decay time keeping constant the frequency of the beats. A model using the pseudospin formalism allows one to attribute the observed quantum beats to the radiative decay of hot trions having two electrons that occupy different energy levels in a QD.

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

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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

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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

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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

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

Daugsch A. Moraes C.S. Fort P. Park Y.K.

出版者

玉川大学ミツバチ科学研究所

雑誌

ミツバチ科学 = Honeybee science (ISSN:03882217)

巻号頁・発行日

vol.27, no.2, pp.55-62, 2007-02 (Released:2011-03-05)

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

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

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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

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

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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.

著者

Taniguchi H. Morita Y. Hatsugai Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, no.13, pp.134417, 2005-04

被引用文献数

6 5

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Based on quantum Monte Carlo calculations, we shall discuss the regime where ferromagnetic correlation isdominant in the two-dimensional t-t8 Hubbard model at a finite temperature. In this model, ferromagnetismcompetes with antiferromagnetism and we reveal how crossover occurs between them at a finite temperature bythe bias-free method. We shall investigate the data in the context of the so-called “low-density ferromagnetism.”The weak-coupling result is also shown and the data are compared with the “Nagaokaferromagnetism.”

著者

Baelus B. J. Kanda A. Peeters F. M. Ootuka Y. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, pp.140502, 2005-04

被引用文献数

30 29

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The temperature dependence of the vortex penetration and expulsion fields in mesoscopic superconducting disks are studied. We experimentally find that the penetration field decreases with increasing temperature for all values of the vorticity. On the other hand, the temperature dependence of the expulsion fields shows two regimes: For some vortex states the expulsion field increases with temperature, while for other states it is almost temperature independent. A numerical study based on the nonlinear Ginzburg-Landau theory confirms that the former regime corresponds to multivortex states and the latter to giant vortex states. The origin of this difference is discussed.

著者

Takeda S. Aoki S. Fukugita M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. 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.074510, 2004-10

被引用文献数

16 23

---

We study the scaling behavior of the step scaling function for SU(3) gauge theory, employing the renormalization-group improved Iwasaki gauge action and the perturbatively improved Lüscher-Weisz gauge action. We confirm that the step scaling functions from the improved gauge actions agree with that previously obtained from the plaquette action within errors in the continuum limit at both weak and strong coupling regions. We also investigate how different choices of boundary counterterms for the improved gauge actions affect the scaling behavior. In the extrapolation to the continuum limit, we observe that the cutoff dependence becomes moderate for the Iwasaki action, if a perturbative reduction of scaling violations is applied to the simulation results. We also measure the low energy scale ratio with the Iwasaki action and confirm its universality.

著者

Aoki S. Fukugita M. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. 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.3, pp.034503, 2004-08

被引用文献数

4

---

We report on a nonperturbative evaluation of the renormalization factors for the vector and axial-vector currents, ZV and ZA, in the quenched domain-wall QCD (DWQCD) with plaquette and renormalization-group-improved gauge actions. We take the Dirichlet boundary condition for both gauge and domain-wall fermion fields on the finite box, and introduce flavor-chiral Ward-Takahashi identities to calculate the renormalization factors. As a test of the method, we numerically confirm the expected relation that ZV~=ZA in DWQCD. Employing two different box sizes for the numerical simulations at several values of the gauge coupling constant g2 and the domain-wall height M, we extrapolate ZV to infinite volume to remove a/L errors. We finally give the interpolation formula of ZV in the infinite volume as a function of g2 and M.

著者

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

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.69, no.9, pp.094512, 2004-05

被引用文献数

5

---

We present a lattice QCD calculation of the heavy quark expansion parameters µpi2 and µG2 for heavy-light mesons and heavy-light-light baryons. The calculation is carried out on a 203×48 lattice at beta=6.0 in the quenched approximation, using the lattice NRQCD action for heavy quarks. We obtain the parameters µpi2 and µG2 in two different methods: a direct calculation of the matrix elements and an indirect calculation through the mass spectrum, and confirm that both the methods give consistent results. We also discuss an application to the lifetime ratios.