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Shu Tanaka, Seiji Miyashita
2007 年 76 巻 10 号 p.
103001
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
In the corner-sharing lattice, magnetic frustration causes macroscopic degeneracy in the ground state, which prevents systems from ordering. However, if the ensemble of the degenerate configuration has some global structure, the system can have a symmetry breaking phenomenon and thus posses a finite temperature phase transition. As a typical example of such cases, the magnetic phase transition of the Ising-like Heisenberg antiferromagnetic model on the kagomé lattice has been studied. There, a phase transition of the two-dimensional ferromagnetic Ising universality class occurs accompanying with the uniform spontaneous magnetization. Because of the macroscopic degeneracy in the ordered phase, the system is found to show an entropy-driven ordering process, which is quantitatively characterized by the number of “weathervane loop” (WL). We investigate this novel type of slow relaxation in regularly frustrated system.
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Hideo Yoshioka, Masahisa Tsuchiizu, Hitoshi Seo
2007 年 76 巻 10 号 p.
103701
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We theoretically investigate the competition between charge-ordered state and Mott insulating state at finite temperatures in quarter-filled quasi-one-dimensional electron systems, by studying dimerized extended Hubbard chains with interchain Coulomb interactions. In order to take into account one-dimensional fluctuations properly, we apply the bosonization method to an effective model obtained by the interchain mean-field approximation. The results show that lattice dimerization, especially in the critical region, and frustration in the interchain Coulomb interactions reduce the charge-ordering phase transition temperature and enlarge the dimer-Mott insulating phase. We also derive a general formula of the Knight shift in the charge-ordered phase and its implication to experiments is discussed.
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Hiroshi Kontani, Masayuki Naito, Dai S. Hirashima, Kosaku Yamada, Jun- ...
2007 年 76 巻 10 号 p.
103702
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We study the origin of the intrinsic spin Hall conductivity (SHC) and the
d-orbital Hall conductivity (OHC) in Pt based on a multiorbital tight-binding model with spin–orbit interaction. We find that the SHC exceeds 1000 h
e−1·Ω
−1 cm
−1 when the resistivity ρ is smaller than ∼10 μΩ cm, whereas it decreases to 300 h
e−1·Ω
−1 cm
−1 when ρ∼100 μΩ cm. In addition, the OHC is still larger than the SHC. The origin of the huge spin Hall effect (SHE) and
d-orbital Hall effect (OHE) in Pt is the “effective Aharonov–Bohm phase” that is induced by the interorbital transition between
dxy- and
dx2−y2-orbitals with the aid of the strong spin–orbit interaction.
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Takanari Kashiwagi, Masayuki Hagiwara, Shojiro Kimura, Zentaro Honda, ...
2007 年 76 巻 10 号 p.
103703
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We have performed electron spin resonance measurements on single crystals of the
S=1 one-dimensional Heisenberg antiferromagnet Ni(C
5H
14N
2)
2N
3(PF
6) in magnetic fields up to about 55 T and at frequencies up to about 2 THz. For both
H||chain and
H⊥chain, we have found that one of the two or three excitation modes that are observed in magnetic fields between the critical field (
Hc) and about 15 T survives in the high-field region. This mode approaches a paramangetic resonance line at high-fields and fits well with the conventional antiferromagnetic resonance mode with easy-plane anisotropy. This result suggests that the spin-excitation modes above
Hc change from modes affected by quantum fluctuations to those expected for a conventional antiferromagnet.
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Kenya Tanaka, Yusuke Kawahito, Yuki Yonezawa, Daisuke Kikuchi, Hidekaz ...
2007 年 76 巻 10 号 p.
103704
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We have succeeded in synthesizing the filled skutterudite Pr
xFe
4Sb
12 with the Pr-site filling fraction
x close to 1 under high pressure. The residual resistivity of ∼24 μΩ·cm is several times smaller than that of samples with
x∼0.8 synthesized under ambient pressure by independent research groups, indicating that highly improved sample quality can be achieved by reducing the Pr-site vacancy. From the transport, magnetic, and thermal measurements of the present sample with
x∼1, we have found a singlet ground state of the crystalline electric field (CEF) for 4
f-electrons and no phase transition down to 0.15 K, in contrast to the reported magnetic ordering near 5 K in the samples with
x∼0.8. The effect of the Pr-site vacancy on the CEF level scheme and the 3
d-electron density of states near the Fermi level is discussed as a possible origin of such a drastic change in the magnetic ground state.
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Yoshiaki Kobayashi, Mai Yokoi, Taketo Moyoshi, Masatoshi Sato
2007 年 76 巻 10 号 p.
103705
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The superconducting transition temperatures of Na
xCoO
2·
yH
2O prepared by various methods have been found to exhibit the systematic dependence on the nuclear quadrupole frequency ν
Q. In the
T–3ν
Q phase diagram, the superconducting region of 3ν
Q, spreading over the region between ∼12.0 and ∼12.9 MHz, is divided into two regions by the nonsuperconducting phase between ∼12.5 and ∼12.6 MHz. We have investigated the origin of the nonsuperconducting phase by detailed measurements of
59Co-NQR and
2D-NMR, and the results indicate that the nonsuperconducting phase is possibly in the charge-density-wave or the charge disproportionate state, in which the magnetic moments induced inhomogeneously by this transition become frozen at low temperatures.
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Masahiro Nagao, Toru Asaka, Takuro Nagai, Daisuke Akahoshi, Ryota Hata ...
2007 年 76 巻 10 号 p.
103706
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We investigated the crystal structures of single-crystal Nd
0.2Sr
0.8MnO
3 by means of synchrotron x-ray diffraction measurement and transmission electron microscopy. We observed the coexistence of distinct crystal-structural phases, i.e., tetragonal (orbital ordered) and cubic (orbital disordered) phases, over a significantly wide range of temperatures. The ratio of these phases varied continuously with temperature. These indicate that the crystal exhibits a diffuse phase transition of the 3
z2−
r2-type orbital ordering. Moreover, we observed the anisotropic evolution of the orbital-ordered nanodomains in the cubic phase. This specific nature of the phase transition probably originates from the competition between the orbital order and disorder.
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Takafumi Sato, Kensei Terashima, Kosuke Nakayama, Hiroaki Matsui, Taka ...
2007 年 76 巻 10 号 p.
103707
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We have performed high-resolution angle-resolved photoemission spectroscopy on high-
Tc superconductors La
1.85Sr
0.15CuO
4 (LSCO) and Bi
2Sr
2CaCu
2O
8+δ (Bi2212) to study the universality of many-body interaction in hole-doped high-
Tc superconductors. We found that the emergence of kink in the dispersion in the off-nodal region at the superconducting state is a common feature, while the energy scale of kink is remarkably different between LSCO and Bi2212. We conclude that the coupling of electrons with spin excitations at the off-nodal region is universal in hole-doped high-
Tc cuprates.
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Akihiro Kondo, Hideki Tou, Masafumi Sera, Fumitoshi Iga, Toshiro Sakak ...
2007 年 76 巻 10 号 p.
103708
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We have studied the effect of Nd doping on phase IV of Ce
0.7Nd
yLa
0.3−yB
6 (
y=0.005, 0.01, 0.03, and 0.05) to obtain information on the order parameter in phase IV. Phase IV is rapidly suppressed and phase III is stabilized by the Nd doping. Phase IV disappears at the critical concentration
yc∼0.015 above which only phase III exists below 1.4 K. The macroscopic properties in phase IV are not affected by the Nd doping. For
y=0.01, there exists a region where phases III and IV coexist at a low magnetic field. This mixed state is unstable and is easily changed to phase III by applying the magnetic field. This indicates that phases III and IV are competitive and phase IV is not the magnetic dipole ordered phase. The long-range ordering temperatures from phase IV or III to the paramagnetic region are constant at least up to
y=0.05. This suggests the existence of some relationship between phases III and IV.
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Yukiaki Ishida, Hiromichi Ohta, Atsushi Fujimori, Hideo Hosono
2007 年 76 巻 10 号 p.
103709
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We have performed a temperature-dependent photoemission study of a Na
xCoO
2 (
x∼0.8) epitaxial thin film prepared by the reactive solid-phase epitaxy method. The chemical potential shift as a function of temperature was derived from the Co 3
d peak shift, and revealed a crossover from the degenerate Fermion state at low temperatures to the correlated hopping state of Co
3+/Co
4+ mixed-valence at high temperatures. This suggests that the large thermoelectric power at high temperatures should be considered in the correlated hopping picture.
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Zhi-An Ren, Junya Kato, Takahiro Muranaka, Jun Akimitsu, Markus Kriene ...
2007 年 76 巻 10 号 p.
103710
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We report superconductivity in heavily boron-doped bulk silicon carbide related to the diamond structure. The compound exhibits zero resistivity and diamagnetic susceptibility below a critical temperature
Tc of ∼1.4 K, and an effective boron doping concentration higher than 10
21 cm
−3. We present the
H–
T phase diagram of this new superconducting compound determined from AC susceptibility. In finite DC magnetic fields a clear hysteresis was observed between cooling and subsequent warming runs. This indicates, in contrast with the type-II superconductivity in boron-doped diamond and silicon, that a type-I superconductivity with a critical field
Hc(0) of about 100 Oe is realized in boron-doped SiC. Moreover, the specific-heat shows a clear jump at
Tc, demonstrating bulk nature of the superconductivity.
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Naokazu Shibata, Kentaro Nomura
2007 年 76 巻 10 号 p.
103711
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We study the ground state properties of the ν=2⁄3 fractional quantum Hall systems basing on the density matrix renormalization group (DMRG) analysis. The ground-state energy and the pair correlation functions are calculated for various spin polarizations. The results indicate the phase separation in partially spin polarized states, where two domains of the spin unpolarized state and the fully spin polarized state are formed. We expect coupling with external degrees of freedom such as nuclear spins is important to realize multi-domain structures in partially spin polarized state.
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Hiromitsu Shimoyama, Macoto Kikuchi
2007 年 76 巻 10 号 p.
103801
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
It is widely accepted that the folding process of a protein is in large part determined by topology of the native structure. A class of coarse-grained model called Go-like model that takes only the native-state topology into account has successfully described folding of many proteins. In this letter, we show that a Go-like model with reduced number of amino acids exhibits a similar free-energy landscape for Ribonuclease H to one obtained by Go-like model. Coarser-grained Go-like model shows a qualitatively same variation of the free-energy landscape due to energy balance between domains.
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Satoshi Morita
2007 年 76 巻 10 号 p.
104001
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
New annealing schedules for quantum annealing are proposed based on the adiabatic theorem. These schedules exhibit faster decrease of the excitation probability than a linear schedule. To derive this conclusion, the asymptotic form of the excitation probability for quantum annealing is explicitly obtained in the limit of long annealing time. Its first-order term, which is inversely proportional to the square of the annealing time, is shown to be determined only by the information at the initial and final times. Our annealing schedules make it possible to drop this term, thus leading to a higher order (smaller) excitation probability. We verify these results by solving numerically the time-dependent Schrödinger equation for small size systems.
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Yoshihiro Yamazaki, Kazuaki Saito, Naoki Kobayashi, Tatsuya Ozawa, Mit ...
2007 年 76 巻 10 号 p.
104002
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
A scaling hypothesis for the standard deviation σ of the height of growing interfaces is proposed by extending the Family–Vicsek (FV) scaling hypothesis. A data-collapsing method is adopted for estimating values of three exponents α, β, and
z, which characterize, respectively, the roughness, growth, and dynamic properties of growing interfaces. The estimation is carried out through σ, which is a function of both the time and the width of the interfaces. The advantages of the present extended scaling hypothesis are as follows: (A) The value of β can be obtained even if the data for σ in terms of
t are few so that its value is not determined precisely from the slope of the lnσ vs ln
t plot. (B) Different scaling relations can be obtained during the time evolution of interface growth. (C) By introducing a new exponent, which represents the time dependence of σ for a short width, a scaling argument is possible even for growing interfaces that do not satisfy the FV scaling relation. Successful applications are carried out to a few numerical models and a paper-wetting experiment.
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Seiji Miyashita
2007 年 76 巻 10 号 p.
104003
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The properties of the conveyance of quantum particles by a moving potential well are studied. We sweep a bell-shape potential well with constant velocity, and study how the potential well traps the particle. In particular, we study the case where we suddenly change the velocity up to a constant velocity. We investigate the number of particles conveyed as a function of the sweep velocity. The effect of the discretization of space in the numerical method is also investigated. We also study how the potential well carries the particle up from a region where the potential energy is low, to another region of high potential energy. Here, we find that the tunneling effect reduces the number of particles carried up. This process is well described by the Landau–Zener mechanism. The dynamics of the density of particles under the sweeping potential well is also studied in noninteracting Fermi particle systems, where the position of the Fermi level plays an important role.
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Yasushi Kondo
2007 年 76 巻 10 号 p.
104004
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We implement a quantum teleportation algorithm in NMR with
13C-labeled L-alanine. Here three
13C-nuclear spins are qubits and H-nuclear spins are employed as a well-defined quantum mechanical interface to a detector. Our experiment is considered as a realization of “quantum teleportation without irreversible detection” and is helpful for understanding the principle of quantum teleportation.
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Hans De Raedt, Koen De Raedt, Kristel Michielsen, Koenraad Keimpema, S ...
2007 年 76 巻 10 号 p.
104005
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
Inspired by Einstein–Podolsky–Rosen–Bohm experiments with photons, we construct an event-based simulation model in which every essential element in the ideal experiment has a counterpart. The model satisfies Einstein’s criterion of local causality and does not rely on concepts of quantum and probability theory. We consider experiments in which the averages correspond to those of a singlet and product state of a system of two
S=1⁄2 particles. The data is analyzed according to the experimental procedure, employing a time window to identify pairs. We study how the time window and the passage time of the photons, which depends on the relative angle between their polarization and the polarizer’s direction, influences the correlations, demonstrating that the properties of the optical elements in the observation stations affect the correlations although the stations are separated spatially and temporarily. We show that the model can reproduce results which are considered to be intrinsically quantum mechanical.
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Takeshi Mizushima, Masanori Ichioka, Kazushige Machida
2007 年 76 巻 10 号 p.
104006
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We theoretically investigate the ground state of trapped neutral fermions with population imbalance in the BCS–BEC crossover regime. On the basis of the single-channel Hamiltonian, we perform full numerical calculations of the Bogoliubov–de Gennes equation coupled with the regularized gap and number equations. The zero-temperature phase diagram in the crossover regime is presented, where the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) pairing state governs the weak-coupling BCS region of a resonance. It is found that the FFLO oscillation vanishes in the BEC side, in which the system under population imbalance turns into a phase separation (PS) between locally binding superfluid and fully polarized spin domains. We also demonstrate numerical calculations with a large particle number
O(10
5), comparable to that observed in recent experiments. The resulting density profile on a resonance yields the PS, which is in good agreement with the recent experiments, while the FFLO modulation exists in the pairing field. It is also proposed that the most favorable location for the detection of the FFLO oscillation is in the vicinity of the critical population imbalance in the weak coupling BCS regime, where the oscillation periodicity becomes much larger than the interparticle spacing. Finally, we analyze the radio-frequency (RF) spectroscopy in the imbalanced system. The clear difference in the RF spectroscopy between BCS and BEC sides reveals the structure of the pairing field and local “magnetization”.
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Daisuke Takahashi, Ryogo Hirota
2007 年 76 巻 10 号 p.
104007
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We propose a new type of multi-soliton solution to the box and ball system which is a completely discrete soliton system. The solution follows a form of ultradiscretized permanent which is defined by a signature-free determinant. Moreover, we show the solution is equivalent to a known type of solution and give a direct proof of solution.
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Masatoshi Sato, Yukiharu Ohsawa
2007 年 76 巻 10 号 p.
104501
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
Electron acceleration caused by small pulses in oblique shock waves in a reversed external magnetic field is studied with theory and particle simulations. Simulations show that after a shock wave has passed a neutral sheet, across which the external magnetic field is reversed, a new density pulse is produced in front of the original shock wave. This pulse quickly evolves into a shock wave with the magnetic polarity opposite to that of the original shock wave. In this secondary shock wave, two types of small pulses are generated. One is compressive, and the other is field reversed. In these small pulses, electron acceleration to ultrarelativistic energies is observed. A theoretical analysis is made on the electron acceleration in field-reversed small pulses that propagate obliquely to a magnetic field. It is confirmed that the simulation results are consistent with the theoretical predictions.
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Mieko Toida, Hiroyuki Higashino, Yukiharu Ohsawa
2007 年 76 巻 10 号 p.
104502
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The propagation of the two types of fast magnetosonic waves, i.e., low- and high-frequency modes, in a two-ion-species plasma is studied theoretically and numerically. It is analytically found that the KdV equation for the low-frequency mode is valid for amplitudes ε<2Δ
ω, where Δ
ω=(ω
+0−ω
−r)⁄ω
+0 with ω
+0 being the cutoff frequency of the high-frequency mode and ω
−r the resonance frequency of the low-frequency mode; Δ
ω is given as a function of the density ratio and cyclotron frequency ratio of two ion species. It is then suggested that nonlinear coupling between the two modes can occur if ε>2Δ
ω. With electromagnetic particle simulations, the evolution of the low- and high-frequency-mode pulses is investigated for various density and cyclotron frequency ratios and is compared with theoretical predictions. In particular, it is shown that high-frequency-mode pulses are generated from a long-wavelength low-frequency-mode pulse if its amplitude ε exceeds 2Δ
ω.
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Hidetsugu Seki, Yasuo Y. Suzuki, Henri Orland
2007 年 76 巻 10 号 p.
104601
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We formulate a self-consistent field theory for polyelectrolyte brushes in the presence of counterions. We numerically solve self-consistent field equations for weak coupling cases and study the monomer density profile, the distribution of counterions, and the total charge distribution. We also study scaling relations for brush height and compare them with the predictions based on other theories. We find a weak dependence of brush height on grafting density. We fit the counterion distribution outside a brush using the Gouy–Chapman solution for a charged virtual plane. We calculate the amount of counterions outside the brush and find that it saturates as the charge of polyelectrolytes increases in a weak coupling case.
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Tatsuya Fujisaki, Yasuhiro Nakazawa, Masaharu Oguni, Kazuya Nakata, Ma ...
2007 年 76 巻 10 号 p.
104602
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The magnetic-field dependences of heat capacities of two-dimensional (2D) network systems consisting of Mn
4 single-molecule magnets are studied at low temperatures between 0.6 and 10 K. Thermal anomalies associated with the formation of the antiferromagnetic order of large spins (
ST=9) mediated by the superexchange interactions are observed at 4.35 K for [Mn
4(hmp)
6{N(CN)
2}
2](ClO
4)
2 (hmp
− = 2-hydroxymethylpyridinate; N(CN)
2− = dicyanamide) and 2.10 K for [Mn
4(hmp)
4Br
2(OMe)
2{N(CN)
2}
2]·2THF·0.5H
2O. They are suppressed by applying weak magnetic fields smaller than 1 T. In the case of [Mn
4(hmp)
4Br
2(OMe)
2{N(CN)
2}
2]·2THF·0.5H
2O, the entropy associated with the magnetic transition almost coincides with that of the ground-state doublet of
Sz=±9. The coexistence of bulk-magnet characters and single-molecule magnet (SMM) characters in this network system gives an intrinsic peak broadening effect that resembles the finite-size effect in the magnetic nanoparticles.
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Kenzo Sasai, Kazuma Hirota, Yohei Nagao, Shigeki Yonezawa, Zenji Hiroi
2007 年 76 巻 10 号 p.
104603
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
Inelastic neutron-scattering and neutron powder-diffraction experiments were carried out to investigate the localized mode, proposed from various bulk measurements, in the β-pyrochlore AOs
2O
6 (A=K, Rb, Cs). The localized mode was identified in all three compounds as well as in another β-pyrochlore CsW
2O
6. The anharmonicity of the mode is weak in RbOs
2O
6 and CsOs
2O
6 but substantial in KOs
2O
6.
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Hiroshi Takatsu, Shingo Yonezawa, Shinichiro Mouri, Satoru Nakatsuji, ...
2007 年 76 巻 10 号 p.
104701
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We report physical properties of the conductive oxide PdCoO
2 in the layered delafossite structure through measurements of the electrical resistivity, specific heat, magnetic susceptibility, polarized Raman spectra and infrared absorption. We observed two prominent Raman peaks at 520 and 712 cm
−1. The presence of these high frequency optical phonons is essential to explain the temperature dependence of the specific heat and the resistivity. No sign of superconductivity was detected in electrical resistivity and AC susceptibility down to 15 mK.
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Yoshihiro Ishibashi, Makoto Iwata, Ahmad M. A. Musleh
2007 年 76 巻 10 号 p.
104702
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The extrapolation length adopted in the Tilley–Zeks model of ferroelectric thin films plays a substantial role in governing the dielectric properties of thin films through the boundary conditions. The boundary conditions under an applied field are reexamined. The exact formulas for the transition temperature, the dielectric susceptibility, and the Curie constant are obtained for the Tilley–Zeks model of ferroelectric thin films, where various combinations of the extrapolation length are taken into account. The polarization profiles obtained under the applied field may be considered to approximately represent the soft mode.
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Makoto Yoshida, Nobuyuki Ogata, Masashi Takigawa, Jun-ichi Yamaura, Ma ...
2007 年 76 巻 10 号 p.
104703
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We report magnetization, nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and transmission electron microscopy (TEM) studies on the quasi-two-dimensional spin-gap system (CuCl)LaNb
2O
7, a possible candidate for the
J1–
J2 model on a square lattice. A sharp single NQR line is observed at the Cu and Cl sites, indicating that both Cu and Cl atoms occupy a unique site. However, the electric field gradient tensors at the Cu, Cl, and La sites do not have axial symmetry. This is incompatible with the reported crystal structure. Thus the
J1–
J2 model has to be modified. We propose alternative two-dimensional dimer models based on the NMR, NQR, and TEM results. The value of the hyperfine coupling constant at the Cu sites indicates that the spin density is mainly on the
d(3
z2−
r2) orbital (
z||
c). At 1.5 K, Cu- and Nb-NMR signals disappear above the critical field
Bc1\\simeq10.3 T determined from the onset of the magnetization, indicating a field-induced magnetic phase transition at
Bc1.
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Satoshi Kawaguchi
2007 年 76 巻 10 号 p.
104704
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
In this paper, we study the effect of Coulomb interaction on current in double quantum dot systems by a perturbative approach. Terms of up to the second-order in the Coulomb interaction are taken into consideration. Under current conservation, zero-bias conductance, the conductance under finite bias and its temperature dependence are investigated. These physical quantities in the absence and presence of Coulomb interaction are compared, and the effect of Coulomb scattering on electron conduction is clarified. For strong interaction, our numerical results are compared with those obtained by other methods. The characteristics and limitations of this perturbative approach are discussed. It is concluded that the delicate inter-dot coupling effect on zero-bias conductance is not well reflected by our perturbative approach.
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Masahiro Shimizu, Hideaki Amanuma, Kenichi Hachitani, Hideto Fukazawa, ...
2007 年 76 巻 10 号 p.
104705
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We report
75As nuclear quadrupole resonance (NQR) measurements of the filled skutterudite superconductors LaRu
4As
12 and PrRu
4As
12. The temperature dependence of the
75As-NQR line and the nuclear spin–lattice relaxation rate 1⁄
T1 show that Pr
3+ has a crystal electric field (CEF) singlet ground state with a separate first excited state. In the superconducting states of PrRu
4As
12 and LaRu
4As
12, 1⁄
T1 has a coherence peak just below the transition temperature and decreases exponentially at low temperatures. This behavior shows that the s-wave superconductivity occurs in both compounds.
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To Sing Li, Chi Hsuan Lee, Ming Fa Lin
2007 年 76 巻 10 号 p.
104706
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
Electronic and transport properties of finite length double-walled carbon nanotubes subject to the influences of a transverse electric field are studied by the tight-binding model. The electric field would modify state energies and modulate energy gap. Effects of intertube interactions on the electronic and transport properties are also investigated. The electronic structures are found to exhibit rich dependence on the field strength, the intertube interactions, and the nanotube length. The variations of state energies with the electric field will also be reflected in the electrical and thermal conductance. The positions of the conductance peaks are strongly dependent on the intertube interactions, and the nanotube length. The heights of the electrical and thermal conductance peaks display the quantized behavior, while those of the Peltier coefficient do not. The different symmetric configurations can be distinguished by the electrical conductance measurements.
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Kazuaki Kobayashi, Kenji Watanabe, Takashi Taniguchi
2007 年 76 巻 10 号 p.
104707
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We calculated the electronic and lattice properties of various hexagonal BN (
h-BN) phases. They are hexagonal layered structures with different stacking sequences. We discuss the effect of the manner of stacking on the electronic band structures. The lattice properties were optimized automatically by the first-principles molecular dynamics (FPMD) method. Their calculated electronic band structures are nonmetallic and most of their band gaps are indirect. They have flat bands at the valence (conduction) band top (bottom) at some symmetry lines in a Brillouin zone (BZ). The positions of the valence band maximum (VBM) and conduction band minimum (CBM) in their electronic band structures are varied by changing the stacking sequences.
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Namjae Kim, Mitsumasa Ishiwata, Toshinori Uehara, Hidenori Yakushiji, ...
2007 年 76 巻 10 号 p.
104708
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
For a few types of relatively small probe molecules with different sizes and geometrical anisotropies, alignment-induced
13C chemical shifts or spacings in the multiplet due to the residual dipolar interaction are measured in the anisotropic S
A and S
C* phases of ferroelectric liquid crystals. On the basis of the simplified motional model, the orientational order parameter and the tilt angle are determined for the probes and compared with those of the liquid crystal itself. The tilt angles of the probes are fairly similar to those of liquid crystals. Various types of temperature variations of the orientational order are discussed in terms of the mobility and spatial distribution of the probe molecules in the smectic layers in relation to the expulsion of the probes from the rigid core region in the liquid crystal.
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Genta Wakita, Yoshikazu Suzumura
2007 年 76 巻 10 号 p.
104709
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The NMR relaxation rate, 1⁄
T1, in one-dimensional Tomonaga–Luttinger model with an open boundary has been investigated to comprehend the electronic state, which depends on
x, the distance from the boundary. Based on the bosonization scheme, we examine the spin response function,
R(
x,
T) [∝1⁄(
T1T)], as the function of
x, temperature (
T) and interaction. It is shown that, with increasing
x,
R(
x,
T) increases from zero with an oscillation and reduces to a finite value after taking a maximum of the peak height. The amplitude of the oscillation is enhanced by interaction but decreases exponentially due to thermal fluctuation. We demonstrate properties associated with the Tomonaga–Luttinger liquid from the view point of the interplay of boundary, interaction and temperature.
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Shinji Tokudomi, Junpei Azuma, Kazutoshi Takahashi, Masao Kamada
2007 年 76 巻 10 号 p.
104710
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
Surface photo-voltage (SPV) effect on
n-type GaAs(100) has been investigated with a newly developed time-resolved photoemission spectroscopy, in which the sample surface is excited by one-photon of the pump pulse and the photoemission is measured by two-photon excitation of the probe pulse. Ultrafast decay of the SPV was found in a several picosecond range at 300 and 100 K, corresponding to the hot-electron lifetime in GaAs. The slow SPV decay was also observed in a few hundred picoseconds, due to the thermalized electrons.
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Tsuneya Ando
2007 年 76 巻 10 号 p.
104711
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The frequency shift and broadening of long-wavelength optical phonons are calculated for varying Fermi level in a bilayer graphene. Symmetric modes with displacements of two layers in phase are affected strongly. In the absence of a magnetic field, the broadening disappears and the frequency shift exhibits a logarithmic singularity when the Fermi energy is a half of the phonon energy, and the shift increases in proportion to the Fermi energy for sufficiently high electron density. In magnetic fields, the broadening is resonantly enhanced and the frequency shift exhibits a rapid change when the phonon energy becomes the energy separation of Landau levels between which optical transitions are allowed.
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Rie Y. Umetsu, Kazuaki Fukamichi, Akimasa Sakuma
2007 年 76 巻 10 号 p.
104712
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
We present magnetic properties, electronic structures and phase stability of
L1
0- and
B2-type MnRh equiatomic alloys. The calculated density of states for the
L1
0-type equiatomic alloy in the collinear antiferromagnetic state exhibits a marked dip around the Fermi energy
EF. The experimental electronic specific heat coefficient γ
e of the
L1
0-type equiatomic alloy is comparatively low of about 5.0 mJ mol
−1 K
−2, verifying the theoretical calculation. The effective exchange constant
J0 in the collinear antiferromagnetic state is given to be about 171.9 meV, corresponding to
TN=1330 K in the molecular field approximation scheme. The theoretical results predict that the antiferromagnetism of the
B2-type equiatomic alloy is unstable, implying that the ground state is very weak ferromagnetic or non-magnetic. On the other hand, the total energy of the
B2-type alloy in the paramagnetic state is lower than that of the
L1
0-type alloy, being consistent with the experimental fact that a diffusionless transformation between the
L1
0- and
B2-type structures occurs below room temperature.
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Hiroshi Wako, Haruo Abe
2007 年 76 巻 10 号 p.
104801
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
The folding of lattice proteins with single amino acid substitutions was studied using a statistical mechanical model for protein folding. All possible single amino acid substitutions were analyzed for two different native conformations, and two amino acid sequences foldable to the given native conformation were considered for each native conformation. First, the transition temperature change Δ
Tm(ξ
i) with the conformational energy change Δ
E(ξ
i) caused by the substitution of the amino acid residue type ξ
i at the
i-th residue was examined. Although both Δ
E(ξ
i) and Δ
Tm(ξ
i) strongly depend on the amino acid sequence (as a result, these two changes for the two proteins with different amino acid sequences foldable to the same native conformation differ considerably from each other), it is indicated that the correlations between Δ
E(ξ
i) and Δ
Tm(ξ
i) for the given residue
i of the two proteins are mainly determined by their native conformations and are less dependent on their amino acid sequences. We classified the residues into three groups according to the coefficient of regression χ
i of Δ
Tm(ξ
i) on Δ
E(ξ
i), i.e., the susceptibility of the conformational stability to the amino acid substitutions. Some of the residues in two of the three groups, which have clear correlations between Δ
E(ξ
i) and Δ
Tm(ξ
i) but have different χ
i’s, are clustered to form domains in the native conformations. The residues in the third group, in which Δ
Tm(ξ
i) is independent of Δ
E(ξ
i), are located in the loop and terminal regions. Secondly, φ(η,ξ
i), which is defined by referring to the Φ value that characterizes the transition state, but into which the progress variable of protein folding η is introduced in this study, was examined for the mutants described above. It is shown that φ(η,ξ
i) can reveal the states of individual amino acid residues and characterize their cooperative behaviors not only in the transition state but also at various stages of the folding process.
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Kumiko Hayashi, Hiroaki Takagi
2007 年 76 巻 10 号 p.
105001
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり
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Yosuke Tanaka, Hidekazu Tanaka, Toshio Ono, Akira Oosawa, Kiyoko Moris ...
2007 年 76 巻 10 号 p.
108001
発行日: 2007/10/15
公開日: 2010/08/12
ジャーナル
認証あり