著者

Okada Susumu Saito Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.16, pp.165410, 2002-04

被引用文献数

74 83

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We report first-principles total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled BN nanotubes, (n,0)@(15,0) and (m,0)@(20,0). We find that the most favorable double-walled nanotubes studied here are (7,0)@(15,0) and (12,0)@(20,0) in which the interwall distances are about 3 Å. The electronic energy bands around the Fermi energy depend interestingly on the tube radii due to the hybridization between σ and π states. We also find that the nearly-free-electron states of the nanotubes induce peculiar charge redistribution in the interwall region.

著者

Okada Susumu

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.72, no.15, pp.153409, 2005-10

被引用文献数

12 9

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Total-energy electronic-structure calculations were performed to explore energetics and electronic structures of a one-dimensional array of C60 and potassium atoms encapsulated in metallic nanotubes. We find that the electron states of the potassium intercalated peapods depend on the number of potassium atoms intercalated. Intercalation induces substantial hybridization between pi electron states of C60 and the nanotube. The local density of states around the Fermi level shows that the potassium intercalated C60-peapod is a novel metal whose carriers are distributed on both the C60 and the nanotube.

著者

Umeda T. Ishitsuka Y. Isoya J. Son N. T. Janzén E. Morishita N. Ohshima T. Itoh H. Gali A.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, pp.193202, 2005-05

被引用文献数

55

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Carbon vacancies (VC) are typical intrinsic defects in silicon carbides (SiC) and so far have been observed only in the form of positively charged states in p-type or semi-insulating SiC. Here, we present electron-paramagnetic-resonance (EPR) and photoinduced EPR (photo-EPR) observations of their negatively charged state (V_C^-) in n-type 4H-SiC. This EPR center (called HEI1) is characterized by an electron spin of 1/2 in a Si-Si antibonding state of VC. First-principles calculations confirm that the HEI1 center arises from V_C^- at hexagonal sites. The HEI1 spectrum shows a transition between C1h and C3v symmetries due to a fast reorientation effect reflected in the nature of this defect. The photo-EPR data suggest that V_C^2- is the dominant form of VC when the Fermi level lies 1.1 eV below the conduction band.

著者

Okada Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.68, no.23, pp.235402, 2003-12

被引用文献数

26

---

We report electronic structures and stabilities of rhombohedral C60 polymers by using the local spin-density approximation in the framework of the density-functional theory. Owing to hybrid networks of sp2-like (threefold coordinated) and sp3-like (fourfold coordinated) carbon atoms, the electronic structures of these polymers are considerably different from that of a face-centered cubic (fcc) C60. We find that polymerized structures attained at the double bonds are semiconducting whereas polymerized structures attained at single bonds are metallic. Significant overlap of the wave function in the space among three adjacent C60 causes the metallic behavior on the latter polymers. We also find that the stacking ordering strongly affects the conducting properties of the metallic polymers. Despite substantial density of states at Fermi level, the C60 polymers do not exhibit any magnetic ordering. Total energy calculations show that the metallic C60 polymers have higher total energy than the semiconducting C60 polymer phases.

著者

Okada Susumu Otani Minoru Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.67, no.20, pp.205411, 2003-05

被引用文献数

96 93

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We report total-energy electronic structure calculations that provide energetics of encapsulation of various fullerenes in carbon nanotubes and electronic structures of resulting carbon peapods. We find that the electron states of the peapods depend on the space in the nanotubes and that they reflect electron states of the encapsulated fullerenes. The deep energy position of the lowest unoccupied state of fullerenes as well as hybridization between π states of the fullerenes and the nearly free-electron states of the nanotubes causes a multicarrier character in the peapods.

著者

Okada Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.87, no.14, pp.146803, 2001-09

被引用文献数

332

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We report first-principles total-energy electronic-structure calculations in the density-functional theory performed for hexagonally bonded honeycomb sheets consisting of B, N, and C atoms. We find that the ground state of BNC sheets with particular stoichiometry is ferromagnetic. Detailed analyses of energy bands and spin densities unequivocally reveal the nature of the ferromagnetic ordering, leading to an argument that the BNC sheet is a manifestation of the flat-band ferromagnetism.

著者

Sugisaki Mitsuru Ren Hong-Wen Nair Selvakumar V. Nishi Kenichi Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.66, no.23, pp.235309, 2002-12

被引用文献数

56 47

---

The effects of external electric and magnetic fields on InP self-assembled quantum dots (QDs) were investigated by means of single dot spectroscopy. By systematically changing a bias applied to the sample, successive energy shifts of the photoluminescence (PL) peaks from excitons and biexcitons due to the quantum confined Stark effect were clearly observed. The quadratic Stark coefficient was evaluated to be of the order of 10-31 Fcm2. The energy separation of the PL peaks arising from the excitons and biexcitons changed with the applied electric field, reflecting a slight difference of the Stark coefficient between the exciton and biexciton states. The existence of permanent dipole moments was also revealed in both the exciton and biexciton states. The spatial separations between the electrons and holes along the growth direction in a QD were estimated to be 7 Å for the exciton state, and 8 Å for the biexciton state. Further, the diamagnetic shift and the Zeeman splitting of the exciton states were clearly observed in a magnetic field. It was found that the diamagnetic coefficient gradually decreases on decreasing the QD size. A simple qualitative model can explain that this result is due to competition between quantum confinement and magnetic confinement.

著者

Tomimoto Shinichi Kurokawa Atsushi Sakuma Yoshiki Usuki Tatsuya Masumoto Yasuaki

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.76, no.20, pp.205317, 2007-11

被引用文献数

14 10

---

Recombination dynamics of excitons confined in disk-shaped InAs/InP quantum dots is studied by time-resolved photoluminescence measurements. By comparing the result with that in a homologous ultrathin quantum well, it is revealed that the lateral confinement of excitons suppresses the thermal variation of the radiative recombination lifetime. The oscillator strength of the radiative transition is reduced with the decrease of the disk height, which is attributed to the increasing tunneling into the InP barrier of the exciton wave function.

著者

Ryu S. Hatsugai Y.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.73, no.24, pp.245115, 2006-06

被引用文献数

134

---

The entanglement entropy (von Neumann entropy) has been used to characterize the complexity of many-body ground states in strongly correlated systems. In this paper, we try to establish a connection between the lower bound of the von Neumann entropy and the Berry phase defined for quantum ground states. As an example, a family of translational invariant lattice free fermion systems with two bands separated by a finite gap is investigated. We argue that, for one-dimensional (1D) cases, when the Berry phase (Zak's phase) of the occupied band is equal to pi×(odd integer) and when the ground state respects a discrete unitary particle-hole symmetry (chiral symmetry), the entanglement entropy in the thermodynamic limit is at least larger than ln 2 (per boundary), i.e., the entanglement entropy that corresponds to a maximally entangled pair of two qubits. We also discuss how this lower bound is related to vanishing of the expectation value of a certain nonlocal operator which creates a kink in 1D systems.

著者

Hosokawa S. Inui M. Kajihara Y. Matsuda K. Ichitsubo T. Pilgrim W. -C. Sinn H. Gonzalez L. E. Gonzalez D. J. Tsutsui S. Baron A. Q. R.

出版者

American Physical Society

雑誌

PHYSICAL REVIEW LETTERS (ISSN:00319007)

巻号頁・発行日

vol.102, no.10, 2009-03

被引用文献数

124

---

The transverse acoustic excitation modes were detected by inelastic x-ray scattering in liquid Ga in the Q range above 9  nm-1 although liquid Ga is mostly described by a hard-sphere liquid. An ab initio molecular dynamics simulation clearly supports this finding. From the detailed analysis for the S(Q, ω) spectra with a good statistic quality, the lifetime of 0.5 ps and the propagating length of 0.4–0.5 nm can be estimated for the transverse acoustic phonon modes, which may correspond to the lifetime and size of cages formed instantaneously in liquid Ga.

著者

Liu S. Y. Ogi Yoshihiro Fuji Takao Nishizawa Kiyoshi Horio Takuya Mizuno Tomoya Kohguchi Hiroshi Nagasono Mitsuru Togashi Tadashi Tono Kensuke Yabashi Makina Senba Yasunori Ohashi Haruhiko Kimura Hiroaki Ishikawa Tetsuya Suzuki Toshinori

出版者

American Physical Society

雑誌

Phsical Review A (ISSN:10502947)

巻号頁・発行日

vol.81, no.3, 2010

被引用文献数

23

---

A time-resolved photoelectron imaging using a femtosecond ultraviolet (UV) laser and a vacuum UV freeelectron laser is presented. Ultrafast internal conversion and intersystem crossing in pyrazine in a supersonic molecular beam were clearly observed in the time profiles of photoioinzation intensity and time-dependent photoelectron images.

著者

Yanagita Tatsuo Kaneko Kunihiko

出版者

American Physical Society

雑誌

PHYSICAL REVIEW LETTERS (ISSN:01433857)

巻号頁・発行日

vol.78, no.22, pp.4297-4300, 1997-06-02

被引用文献数

23

---

A phenomenological model for cloud dynamics is proposed, which consists of the successive operations of the physical processes: buoyancy, diffusion, viscosity, adiabatic expansion, fall of a droplet by gravity, descent flow dragged by the falling droplet, and advection. Through extensive simulations, the phases corresponding to stratus, cumulus, stratocumulus, and cumulonimbus are found by changing the ground temperature and the moisture of the air. They are characterized by order parameters such as the cluster number, perimeter-to-area ratio of a cloud, and Kolmogorov-Sinai entropy. Though our model is simple and constructive, it may shed some light on the true nature of clouds.

著者

Koga Takaaki Nitta Junsaku Akazaki Tatsushi Takayanagi Hideaki

出版者

American Physical Society

雑誌

Physical Review Letters (ISSN:00319007)

巻号頁・発行日

vol.89, no.4, pp.046801-1-046801-4, 2002-07

被引用文献数

451

---

We have investigated the values of the Rashba spin-orbit coupling constant α in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells using the weak antilocalization (WAL) analysis as a function of the structural inversion asymmetry (SIA) of the quantum wells. We have found that the deduced α values have a strong correlation with the degree of SIA of the quantum wells as predicted theoretically. The good agreement between the theoretical and experimental values of α suggests that our WAL approach for deducing α values provides a useful tool in designing future spintronics devices that utilize the Rashba spin-orbit coupling.

著者

Faniel S. Matsuura T. Mineshige S. Sekine Y. Koga T.

出版者

American Physical Society

雑誌

Physical Review B (ISSN:10980121)

巻号頁・発行日

vol.83, no.11, pp.115309, 2011-03-15

被引用文献数

48

---

We report the determination of the intrinsic spin-orbit interaction (SOI) parameters for In0.53Ga0.47As/In0.52Al0.48As quantum wells (QWs) from the analysis of the weak antilocalization effect. We show that the Dresselhaus SOI is mostly negligible in this system and that the intrinsic parameter for the Rashba effect, a_[SO] ≣ 1 α/< Ez >, is given to be a_[SO]m*/m_[e] = (1.46-1.51 x 10^[-17] N_[S] [m^[-2]]) e Å^[2], where α is the Rashba SOI coefficient, < Ez > is the expected electric field within the QW, m*/m_[e] is the electron effective mass ratio, and N_[S] is the sheet carrier density. These values for a_[SO]m* were also confirmed by the observation of beatings in the Shubnikov-de Haas oscillations in our most asymmetric QW sample.

著者

ONORATO M

出版者

American Physical Society

雑誌

PHYSICAL REVIEW LETTERS (ISSN:00319007)

巻号頁・発行日

vol.102, no.11, 2009-03

被引用文献数

2

---

We discuss two independent, large scale experiments performed in two wave basins of different dimensions in which the statistics of the surface wave elevation are addressed. Both facilities are equipped with a wave maker capable of generating waves with prescribed frequency and directional properties. The experimental results show that the probability of the formation of large amplitude waves strongly depends on the directional properties of the waves. Sea states characterized by long-crested and steep waves are more likely to be populated by freak waves with respect to those characterized by a large directional spreading.

著者

原 和彦 金 信弘 大川 英希 佐藤 構二 受川 史彦 ATLAS Collaboration Hara K. Kim S.H. Okawa H. Sato K. Ukegawa F.

出版者

American Physical Society

雑誌

Physical Review D (ISSN:24700010)

巻号頁・発行日

vol.97, no.5, 2018-03-27

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A search for electroweak production of supersymmetric particles in scenarios with compressed mass spectra in final states with two low-momentum leptons and missing transverse momentum is presented. This search uses proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015-2016, corresponding to 36.1 tb(-1) of integrated luminosity at root s = 13 TeV. Events with same flavor pairs of electrons or muons with opposite electric charge are selected. The data are found to be consistent with the Standard Model prediction. Results are interpreted using simplified models of R-parity conserving supersymmetry in which there is a small mass difference between the masses of the produced supersymmetric particles and the lightest neutralino. Exclusion limits at 95% confidence level are set on next-to-lightest neutralino masses of up to 145 GeV for Higgsino production and 175 GeV for wino production, and slepton masses of up to 190 GeV for pair production of sleptons. In the compressed mass regime, the exclusion limits extend down to mass splittings of 2.5 GeV for Higgsino production, 2 GeV for wino production, and 1 GeV for slepton production. The results are also interpreted in the context of a radiatively-driven natural supersymmetry model with nonuniversal Higgs boson masses.

著者

原 和彦 金 信弘 大川 英希 佐藤 構二 受川 史彦 ATLAS Collaboration Hara K. Kim S.H. Okawa H. Sato K. Ukegawa F.

出版者

American Physical Society

雑誌

Physical Review D (ISSN:24700010)

巻号頁・発行日

vol.98, no.3, 2018-08-15

---

Results from a search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) are presented. The analysis uses a data sample corresponding to 36.1 fb(-1) of proton-proton collisions delivered by the Large Hadron Collider at root s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying taus are designed to target a range of supersymmetric scenarios that can be either enriched in or depleted of events involving the production and decay of a Z boson. Data yields are consistent with Standard Model expectations and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge mediated supersymmetry, where Higgsino masses are excluded up to 295 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.46, 1.06, and 2.25 TeV are placed on wino, slepton and gluino masses, respectively.

著者

Souma S. Sawada A. Chen H. Sekine Y. Eto M. Koga T.

出版者

American Physical Society

雑誌

Physical review applied (ISSN:23317019)

巻号頁・発行日

vol.4, no.3, pp.34010, 2015-09-29

被引用文献数

14

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We propose a lateral spin-blockade device that uses the interband Rashba effect in a symmetric double quantum well (QW), where the Rashba effect in the conventional sense vanishes because of its inversion symmetry. The interband Rashba effect manifests itself in the off-diagonal term (represented by the parameter eta) in the QW space using the bonding and antibonding basis [Esmerindo Bernardes, John Schliemann, Minchul Lee, J. Carlos Egues, and Daniel Loss, Phys. Rev. Lett. 99, 076603 (2007)]. In such a system, spin selection is possible by tuning the device length, gate electric field and in-plane magnetic field. We particularly show illustrative mechanisms using a one-dimensional model with k = (k(F), 0), where the selected spin can be blocked completely in the presence of the in-plane magnetic field. While the inclusion of the finite k(y) and/or the gate electric field deteriorates the spin polarization P, finite values remain for P (P>11%). Our proposal can also be regarded as an effective way of enhancing a variation of the Rashba-Edelstein effect, the generation of bulk spin polarization by electric current, based on semiconductor band engineering technology.

著者

Sugawara Y. Wright O. B. Matsuda O. Takigahira M. Tanaka Y. Tamura S. Gusev2 V. E.

出版者

American Physical Society

雑誌

PHYSICAL REVIEW LETTERS (ISSN:00319007)

巻号頁・発行日

vol.88, no.18, pp.185504, 2002-04-18

被引用文献数

106

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We present a new method for imaging surface phonon focusing and dispersion at frequencies up to 1 GHz that makes use of ultrafast optical excitation and detection. Animations of coherent surface phonon wave packets emanating from a point source on isotropic and anisotropic solids are obtained with micron lateral resolution. We resolve rounded-square shaped wave fronts on the (100) plane of LiF and discover isolated pockets of pseudosurface wave propagation with exceptionally high group velocity in the (001) plane of TeO2. Surface phonon refraction and concentration in a minute gold pyramid is also revealed.

著者

原 和彦 佐藤 構二 受川 史彦 ATLAS Collaboration Kazuhiko HARA Koji SATO Fumihiko UKEGAWA

出版者

American Physical Society

雑誌

Physical review D (ISSN:24700010)

巻号頁・発行日

vol.101, no.1, 2020-01

---

Combined measurements of Higgs boson production cross sections and branching fractions are presented. The combination is based on the analyses of the Higgs boson decay modes H→γγ, ZZ∗, WW∗, ττ, b¯b, μμ, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to 79.8  fb−1 of proton–proton collision data collected at √s=13  TeV with the ATLAS detector are used. Results are presented for the gluon–gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be μ=1.11+0.09−0.08. The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5σ (5.3σ). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified minimal supersymmetric Standard Model. No significant deviations from Standard Model predictions are observed.