著者

Nakayama K. Sato T. Dobashi T. Terashima K. Souma S. Matsui H. Takahashi T. Campuzano J. C. Kudo K. Sasaki T. Kobayashi N. Kondo T. Takeuchi T. Kadowaki K. Kofu M. Hirota K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.74, pp.054505, 2006-08

被引用文献数

26

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We have performed systematic angle-resolved photoemission spectroscopy (ARPES) on single-layered cuprate superconductor Bi2Sr2CuO6+delta to elucidate the origin of shadow band. We found that the shadow band is exactly the c(2×2) replica of the main band irrespective of the carrier concentration and its intensity is invariable with respect to temperature, doping, and substitution constituents of block layers. This result rules out the possibility of antiferromagnetic correlation and supports the structural origin of shadow band. ARPES experiments on optimally doped La1.85Sr0.15CuO4 also clarified the existence of the c(2×2) shadow band, demonstrating that the shadow band is not a unique feature of Bi-based cuprates. We conclude that the shadow band is related to the orthorhombic distortion at the crystal surface.

著者

Yamamoto T Mizoguchi T Tanaka I

出版者

AMERICAN PHYSICAL SOC

雑誌

PHYSICAL REVIEW B (ISSN:10980121)

巻号頁・発行日

vol.71, no.24, 2005-06

被引用文献数

48 51

著者

Okada Susumu Miyamoto Yoshiyuki Saito Mineo

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.64, no.24, pp.245405, 2001-11

被引用文献数

48 46

---

We report on a first-principles total-energy calculation that provides the energetics and electronic structure of stable polymerized fullerites consisting of the smallest fullerene C20. We find that the C20 fullerene has periodic three-dimensional covalent networks with orthorhombic and tetragonal symmetries. Both are found to be energetically stable and to be elemental semiconductors with a moderate energy gap of about 1.5 eV. Substantially high peaks of the density of states are found to appear below the top of the valence band, suggesting that these materials under hole-doped conditions are candidates for superconductors.

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.64, no.20, pp.201303, 2001-10

被引用文献数

33 39

---

We report first-principles total-energy electronic-structure calculations that provide energetics of encapsulation of C60 in nanotubes consisting of boron and nitrogen atoms and electronic structures of resulting “BNC peapods.” We find that the encapsulating process is exothermic for (10,10) and (9,9) nanotubes. The energy gain upon the encapsulation is larger than that for carbon peapods, so that the BN nanotube is a promising candidate to accommodate the fullerenes inside. The material is predicted to be a new form of ternary semiconductor with interesting structural hierarchy.

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

---

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

Umeda T. Isoya J. Morishita N. Ohshima T. Kamiya T. Gali A. Deák P. Son N. T. Janzén E.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.70, pp.235212, 2004-12

被引用文献数

50

---

The carbon vacancy is a dominant defect in 4H-SiC, and the "EI5" electron-paramagnetic-resonance (EPR) spectrum originates from positively charged carbon vacancies (VC+) at quasicubic sites. The observed state for EI5, however, has been attributed to a motional-averaged state with the C3v symmetry, and its true atomic structure has not been revealed so far. We here report low temperature (<40 K) EPR measurements on EI5 and show that this center has a C1h-symmetric structure due to Jahn-Teller distortion. We also performed ab inito calculations of the hyperfine tensors for EI5, and obtained a good agreement between experiment and theory in not only their principal values but also their principal axis directions. A good agreement was also demonstrated for the EI6 center (hexagonal-site VC+) in this paper. The transition from EI5(C1h) to EI5(C3v) was found to be thermally activated and its activation energy was measured as 0.014 eV.

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

---

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

---

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

---

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

---

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

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

138

---

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

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/&lt; Ez &gt;, 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, &lt; Ez &gt; 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

Ihara Y. Noda K. Kawamoto A.

出版者

American Physical Society

雑誌

Physical Review B (ISSN:10980121)

巻号頁・発行日

vol.90, no.4, pp.41107, 2014-07-25

被引用文献数

6

---

The local electronic state at every crystallographically independent molecular site was separately investigated in the organic superconductor alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) using site-selective C-13-NMR spectroscopy. The density of states (DOS) at three molecular sites shows independent temperature variation, which is caused by the long-range Coulomb interaction. Comparing the present results with those for a nonsuperconducting counterpart alpha-(BEDT-TTF)(2)RbHg(SCN)(4), we found that the uniform DOS at two of three independent molecular sites is crucial to induce superconductivity. Taking the site-dependent DOS as a parameter, we constructed a phase diagram for a superconductor with long-range Coulomb interaction, an alpha-type BEDT-TTF family, and summarized the competition between charge instability and superconductivity.

著者

Itami T. Munejiri S. Masaki T. Aoki H. Ishii Y. Kamiyama T. Senda Yasuhiro

出版者

The American Physical Society

雑誌

Physical Review B (ISSN:10980121)

巻号頁・発行日

vol.67, no.6, 2003-02-01

---

金沢大学理学部The structure of liquid Sn was studied by neutron scattering experiments in the widest temperature range that was ever performed. Though, on increasing temperature, the existence of the shoulder in the structure factor, S(Q), becomes less clear in the change of the overall shape of the S(Q), the structure related to this shoulder seems to be present even at 1873 K. The first-principle molecular-dynamics ~FPMD! simulation was performed for the first time for liquid Sn by using the cell size of 64 particles. The calculated results well reproduced S(Q) obtained by the neutron experiments. The angle distribution, g(3)(u ,rc), was evaluated for the angle between vectors from centered atom to other two atoms in spheres of cutoff radii rc's. The g(3)(u ,rc) shows that, with the decrease of rc from 0.4 to 0.3 nm, a rather sharp peak around 60 ° disappears and only a broad peak around 100 ° remains; the former peak may be derived from the feature of the closely packed structures and the latter one is close to the tetrahedral angle of 109 °. In addition, the coordination number, n, of liquid Sn counted within the sphere of rc50.3 nm is found to be 2–3 and does not change with the increase of temperature even up to 1873 K. These facts indicate that at least the fragment of the tetrahedral unit may be essentially kept even at 1873 K for liquid Sn. For comparison, the FPMD simulation was performed for the first time also for liquid Pb. No sign of the existence of the tetrahedral structure was observed for liquid Pb. Unfortunately, the self-diffusion coefficients, D's, obtained from this FPMD for liquid Sn do not agree with those obtained by the microgravity experiments though the structure factors, S(Q)'s, are well reproduced. To remove the limitation of the small cell size of the FPMD, the classical molecular-dynamics simulations with a cell size of 2197 particles were performed by incorporating the present experimental structural information of liquid Sn. Obtained D's are in good agreement with the microgravity data.

著者

Hamamoto Yuji Kawarabayashi Tohru Aoki Hideo Hatsugai Yasuhiro

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.88, no.19, pp.195141, 2013-11

被引用文献数

2 1

---

Motivated by the recent experiments indicating a spin-unpolarized ν=0 quantum Hall state in graphene, we theoretically investigate the ground state based on the many-body problem projected onto the n=0 Landau level. For an effective model with the on-site Coulomb repulsion and antiferromagnetic exchange couplings, we show that the ground state is a doubly degenerate spin-resolved chiral condensate in which all the zero-energy states with up spin are condensed into one chirality, while those with down spin to the other. This can be exactly shown for an Ising-type exchange interaction. The charge gap due to the on-site repulsion in the ground state is shown to grow linearly with the magnetic field, in qualitative agreement with the experiments.

著者

Shimada Takahiro Ueda Taku Wang Jie Kitamura Takayuki

出版者

American Physical Society

雑誌

Physical Review B (ISSN:10980121)

巻号頁・発行日

vol.87, no.17, 2013-05

被引用文献数

63

---

The nature of intrinsic point defects, i.e., energetic, ferroelectric, and electronic properties of vacancies in ferroelectric PbTiO_{3}, is studied using first-principles calculations based on the hybrid Hartree-Fock density functional, which correctly reproduces the band gap and thus provides the accurate defect electronic states. The oxygen vacancies are found to behave as double shallow donors and are thermodynamically stable over a wide range of Fermi levels under oxygen-poor conditions, while Pb vacancies are likely to be formed under oxygen-rich conditions and act as double shallow acceptors, which lead to p-type conductivity. The result shows good consistency with the relevant experimental observations. The ferroelectric distortion is disturbed anisotropically outward by oxygen vacancies and is characterized by localized defect electronic states contributed by d orbitals. In contrast, an isotropically inward ferroelectric disturbance is found around Pb and Ti vacancies. Such a ferroelectric disturbance is strongly enhanced by the charging of vacancies, except for Pb vacancies that induce delocalized defect states.

著者

Nemoto Yuya Hino Ken-ichi Maeshima Nobuya

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.87, no.20, pp.205305, 2013-05

被引用文献数

5

---

We examine a continuum effect of a dynamic Wannier-Stark ladder (DWSL) driven by a cw laser—with Fac and ω as amplitude and frequency, respectively—by means of an excess density of states (DOS), ρ(ex)(E), closely related to the more familiar DOS and proportional to the lifetime of a resonance state. It is mathematically shown that ρ(ex)(E) is governed by three different physical mechanisms: the single-channel resonance mechanism, the multichannel nonresonance mechanism, and the multichannel resonance mechanism. The last mechanism becomes more important with the increase in Fac. The effect of the interchannel interaction is maximized when the ratio of a Bloch frequency to ω, represented as η, equals unity. In the actual calculations based on the R-matrix Floquet theory, it is revealed that, in a large-Fac region, ρ(ex)(E) for η=1 shows a complicated spectral structure composed of a couple of newly growing peaks, in contrast to ρ(ex)(E) for η=3 which just shows a monotonic change of a single spectral peak. It is speculated that the pronounced feature of the former spectra is attributed to the Fano-like multichannel resonance mechanism, whereas the feature of the latter case is attributed to the multichannel nonresonance mechanism.