著者

Hara K. Baccehtta N. Spalding W.J. Worm S.D.

出版者

Elsevier B.V.

雑誌

Nuclear instruments & methods in physics research. Section A (ISSN:01689002)

巻号頁・発行日

vol.699, pp.84-88, 2013-01

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On September 30, 2011, the Collider Detector at Fermilab (CDF) finished physics data-taking at the Tevatron proton–antiproton collider. The original CDF silicon tracking detector, proposed in 1981 (SVX) and later replaced and updated (SVX′), was again replaced for Run-2 in 2002–2011 (SVX-II, ISL, L00). These systems operated successfully for many years, performing essential roles in exploring physics at the energy frontier, most notably the discovery of the top quark.

著者

Miyamoto Sadaaki Mukaidono Masao

雑誌

IFSA'97 Prague : proceedings [of the] seventh International Fuzzy Systems Association World Congress

巻号頁・発行日

pp.86-92, 1997-06

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the seventh International Fuzzy Systems Association World Congress, June 25-29, 1997, University of Economics, Prague, Czech Republic

著者

Miyamoto Sadaaki Suizu Daisuke

雑誌

Proceedings of the 1st International Conference on Fuzzy Systems and Knowledge Discovery

巻号頁・発行日

vol.FSDK'02; 2, pp.656-660, 2002-11

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Algorithms of fuzzy c-means clustering with kernels employed\nin nonlinear transformations into high dimensional\nspaces in the support vector machines are studied. The objective\nfunctions in the standard method and the entropy\nbased method are considered and iterative solutions in the\nalternate optimization algorithm are derived. Explicit cluster\ncenters in the data space are not obtained by this method\nin general but fuzzy classification functions are useful which\nhave much more information than crisp clusters in the hard\nc-means. Numerical examples using radial basis kernel functions\nare given.

著者

Zhao Jialong Nair Selvakumar V. Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.3, pp.033307, 2001-01

被引用文献数

7 11

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The size dependence of excitonic states and vibrational modes in CuCl cubic quantum dots embedded in NaCl crystals was studied by means of site-selective persistent spectral hole burning spectroscopy. It is shown that the interaction of the longitudinal optical (LO) phonon with the exciton results in the formation of coupled exciton-phonon modes when the energy of the LO phonon approaches the energy spacings between the ground and excited states of the exciton. The energy anticrossings of the LO phonon modes with two higher optically allowed excited states of the exciton in CuCl QD’s were clearly observed at confinement energies of about 10 and 6 meV, respectively. In addition, the linewidth of the LO phonon sideband in CuCl QD’s in NaCl crystals was found to increase abruptly from 0.3 meV to about 1.2 meV at a confinement energy of about 23 meV, which appears to result from the exciton-phonon mixing of the LO phonon mode with the first excited state of the exciton. The experimental results are qualitatively understood by the LO phonon renormalization theory.

著者

Ignatiev Ivan V. Kozin Igor E. Davydov Valentin G. Nair Selvakumar V. Lee Jeong-Sik Ren Hong-Wen Sugou Shigeo Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.7, pp.075316, 2001-02

被引用文献数

38 48

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Phonon resonances observed in the photoluminescence (PL) spectra of InP and In0.35Ga0.65As self-assembled quantum dots (QD’s) in an external electric field are studied in detail. The resonances are shown to arise from fast phonon-assisted relaxation of hot carriers, and to become observable when the PL is quenched by nonradiative losses from excited states. A simple model is developed that considers tunneling of the carriers from the QD’s into the barrier layer as the main process responsible for PL quenching in the presence of an electric field. From this model, the depth of the potential well for holes is estimated to be 10–20 meV for the InP QD’s. The PL kinetics measurement is performed with a time resolution of 6 ps. Clear evidence of surprisingly fast carrier relaxation with emission of high-energy acoustic phonons is found. Further acceleration of the carrier relaxation is observed under strong optical pumping. We consider this effect to be caused by Auger-like carrier-carrier scattering processes. Acceleration of the relaxation observed at elevated temperatures is ascribed to stimulated phonon emission.

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

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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

Matsumoto Takahiro Suzuki Jun-ichi Ohnuma Masato Kanemitsu Yoshihiko Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.19, pp.195322, 2001-05

被引用文献数

62

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The optical absorption spectrum in nanocrystalline silicon (n-Si) was determined from both light transmittance and reflectance measurements. We observed that n-Si has a phonon structure in the optical absorption spectrum. This structure originates from momentum-conserving TO phonon absorption and emission, and provides direct evidence that n-Si is an indirect-band-gap semiconductor with quantum size effects. By using small-angle x-ray scattering to measure the nanocrystal size distribution, we found that the band-gap widening varies as (1/L)1.6 with decreasing nanocrystal diameter L.

著者

Tokunaga Eiji Ivanov A. L. Nair Selvakumar V. Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.63, no.23, pp.233203, 2001-06

被引用文献数

11 6

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We report observation of the inverse polariton series and a detailed experimental study of the exciton components in polaritons (Hopfield coefficients). Spontaneous emission of excitonic molecules into outgoing polaritons associated with the i(=1,2,3,4,5)th exciton states in bulk CuCl is detected and analyzed by the bipolariton model. Because the intensities of the emission lines, which form the inverse polariton series, are determined by the exciton components in the final-state polaritons, we are able to measure the Hopfield coefficients for the highly composite outgoing polaritons. Quantum interference in the optical decay of excitonic molecules, due to the multiple exciton components in the polariton and biexciton states, is also demonstrated.

著者

Tokunaga Eiji Kurihara Kazuyoshi Baba Motoyoshi Masumoto Yasuaki Matsuoka Masahiro

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.64, no.4, pp.045209, 2001-07

被引用文献数

10 9

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Radiative decay of biexcitons wave-vector (K) selectively generated in a low-K region (0<~

著者

新谷 由紀子 菊本 虔

巻号頁・発行日

pp.1-100, 2010-04

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科研費(課題番号21530822:2009-2011):H21年度実績報告書

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

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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

Cuong Nguyen Thanh Otani Minoru Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.101, no.23, pp.233106, 2012-12

被引用文献数

10 1

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Based on the first-principles total-energy calculations, we demonstrate the possibility of controlling the band-gap and carrier type of bilayer graphene using ionic molecules. Our calculations suggest that bilayer graphene sandwiched by a pair of cation-anion molecules is a semiconductor with a moderate energy gap of 0.26 eV that is attributable to the strong local dipole field induced by the cation-anion pair. Furthermore, we can control the semiconducting carrier type—intrinsic, p-type, or n-type—of bilayer graphene sandwiched by ionic molecules by changing the cation-anion pair.

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

16

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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

Gerlovin I. Ya. Dolgikh Yu. K. Eliseev S. A. Ovsyankin V. V. Efimov Yu. P. Petrov V. V. Ignatiev I. V. Kozin I. E. Masumoto Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.3, pp.035317, 2002-01

被引用文献数

21 17

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Picosecond kinetics of polarized resonant photoluminescence (PL) of HH excitons in the GaAs/AlGaAs superlattices is studied in an external magnetic field. The measurements were made in real time using a streak camera. For the magnetic field aligned along the heterostructure growth direction, the resonant PL exhibits oscillations in the degree of linear polarization. The oscillations are ascribed to quantum beats between sublevels of the optically active excitonic doublet split by the magnetic field. For the magnetic field aligned along the plane of the layers, the resonant PL is found to exhibit oscillations in circular polarization. These oscillations are related to beats between states of the optically active and optically inactive excitonic doublets. Experimental dependence of the oscillation frequency on the magnetic field strength and orientation has allowed us to determine the hole and electron g factors and the electron-hole exchange energy. Dynamics of the degree of circular polarization of the PL in magnetic field is used to measure the energy relaxation rate of the exciton spin states. In the magnetic field exceeding 1 T, the energy relaxation rate is shown to be magnetic-field independent and equal (1±0.2)×1010 s-1. This value is found to be much smaller than the spin phase relaxation rate determined from decay of the quantum beats in linear polarization. Unlike the energy relaxation rate, the latter grows linearly with the field strength and equals (5±0.5)×1010 s-1 at 5 T. It is concluded that the main mechanism responsible for loss of macroscopic spin coherence is the reversible dephasing within inhomogeneously broadened system.

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