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Toshiya Takami, Jun Maki, Jun-ichi Ooba, Taizo Kobayashi, Rie Nogita, ...
2007 Volume 76 Issue 1 Pages
013001
Published: January 15, 2007
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We present a new methodology for analyzing complicated multiphysics simulations by introducing a fictitious parameter. Using the method, we study the quantum mechanical aspects of an organic molecule in water. The simulation is variationally constructed from the
ab initio molecular orbital method and classical statistical mechanics, with the fictitious parameter representing the coupling strength between solute and solvent. We obtain a number of one-electron orbital energies of the solute molecule derived from the Hartree–Fock approximation, and eigenvalue statistical analysis developed in the study of nonintegrable systems is applied to them. On the basis of the results, we analyze the localization properties of the electronic wavefunctions under the influence of the solvent.
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Kazue Kudo, Michinobu Mino, Katsuhiro Nakamura
2007 Volume 76 Issue 1 Pages
013002
Published: January 15, 2007
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The domain patterns in a thin ferromagnetic film are investigated in both experiments and numerical simulations. Magnetic domain patterns under a zero field are usually observed after an external magnetic field is removed. It is demonstrated that the characteristics of the domain patterns depend on the decreasing rate of the external field, although it can also depend on other factors. Our numerical simulations and experiments show the following properties of domain patterns: a sea-island structure appears when the field decreases rapidly from the saturating field to the zero field, while a labyrinth structure is observed for a slowly decreasing field. The mechanism of the dependence on the field sweeping rate is discussed in terms of the concepts of crystallization.
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Akihiro Kondo, Hideki Tou, Masafumi Sera, Fumitoshi Iga
2007 Volume 76 Issue 1 Pages
013701
Published: January 15, 2007
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We have studied the effect of the
Oxy-antiferro-quadrupole (AFQ),
Txyz-antiferro-octupole (AFO), and AF exchange interactions on the Γ
5u-AFO order, which is a strong candidate of the order in phase IV of Ce
xLa
1−xB
6, by mean field calculation for the two-sublattice model. The magnetic phase diagram obtained by the calculation seems to reproduce those of Ce
xLa
1−xB
6, which seems to provide some clues to understanding phase IV. However, a peak of the magnetic susceptibility disappears easily after introducing the
Oxy-AFQ interaction, which is because the
Oxy-FQ order that accompanies the Γ
5u-AFO order is easily suppressed by the
Oxy-AFQ interaction. The present work indicates that in order to understand the physics of Ce
xLa
1−xB
6, further studies are necessary both experimentally and theoretically.
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Hajime Takayama, Koji Hukushima
2007 Volume 76 Issue 1 Pages
013702
Published: January 15, 2007
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The field-cooled (FC) process on an Ising spin-glass model is investigated by a standard Monte Carlo (MC) method, and the equilibrium magnetization of the same system is evaluated by the exchange MC method. The two types of simulation reveal intriguing glassy (nonequilibrium) dynamic properties of the FC magnetization (FCM) of the system. In particular, the FCM decrease is observed when the FC process is halted at a low temperature, although its value is smaller than the corresponding equilibrium value. We present a comprehensive interpretation of such peculiar phenomena on the basis of the scenario for the FCM process recently proposed by Jönsson and one of us (HT).
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Kenji Harada, Naoki Kawashima, Matthias Troyer
2007 Volume 76 Issue 1 Pages
013703
Published: January 15, 2007
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The quasi-one-dimensional
S=1 Heisenberg antiferromagnet with a biquadratic term is investigated at zero temperature by quantum Monte Carlo simulation. As the magnitude of the inter-chain coupling is increased, the system undergoes a phase transition from a spontaneously dimerized phase to a Néel ordered or spin nematic phase. The numerical results suggest the possibility of an unconventional second-order transition in which the symmetry group characterizing one phase is not a subgroup of the other.
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Masahito Mochizuki, Masao Ogata
2007 Volume 76 Issue 1 Pages
013704
Published: January 15, 2007
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In order to understand the experimentally proposed phase diagrams of Na
xCoO
2·
yH
2O, we theoretically study the CoO
2-layer-thickness dependence of its magnetic and superconducting (SC) properties by analyzing a multiorbital Hubbard model using the random phase approximation. When the Co valence
s is +3.4, we show that the magnetic fluctuation exhibits a strong layer-thickness dependence, where it is enhanced at finite (zero) momentum in the thicker (thinner) layer system. A magnetic order phase appears sandwiched by two SC phases, consistent with the experiments. These two SC phases have different pairing states, where one is the singlet extended
s-wave state and the other is the triplet
p-wave state. On the other hand, only a triplet
p-wave SC phase with a dome-shaped behavior of
Tc is predicted when
s=+3.5, which is also consistent with the experiments. Controversial experimental results on the magnetic properties are also discussed.
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Fumihiko Matsui, Tomohiro Matsushita, Yukako Kato, Fang Zhun Guo, Hiro ...
2007 Volume 76 Issue 1 Pages
013705
Published: January 15, 2007
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Two-dimensional photoelectron intensity angular distributions of the graphite valence band were measured using circularly polarized soft X-ray with a photon energy of 500 eV. Photoelectron intensity from the bottom of the 2
s band was observed at the Γ point of
every other Brillouin zone reflecting the photoelectron structure factor, that corresponds to the interference of photoelectron waves from 2
s atomic orbitals within a unit cell. Simultaneously, the circular dichroism of photoelectron forward focusing peak rotation around the incident-light axis was observed. This rotation in the photoelectron intensity angular distribution from the 2
pxy band was about twice those from 2
s and 2
pz bands, reflecting the difference in orbital angular momentum of each band. Taking advantage of the forward focusing peak as a site-specific probe, the local orbital angular momentum of each valence band was analyzed. The origin of the dual behavior that appeared in the observation of
local angular momentum from a
delocalized valence band is discussed in conjunction with the dispersion and spatial origin of the electron.
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Yasuo Narumi, Ken-ichi Suga, Koichi Kindo, Tomoaki Yamasaki, Masayuki ...
2007 Volume 76 Issue 1 Pages
013706
Published: January 15, 2007
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High-field magnetization measurements on BaVS
3 revealed a metamagnetic transition at
B<
BM\\simeq50 T to a newly identified field-induced ferromagnetic phase, which bears the magnetic moment of ∼0.4 μ
B/V, approximately half of the saturation magnetization expected for
S=1⁄2. The transition is associated with an essential change in the electronic state to a
poor conductor, where the gapped
A1g band remains open and only the poor conductivity of nearly localized
Eg electrons is recovered by the field. Based on the magnetization results, a field-temperature phase diagram is proposed for BaVS
3.
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Hitoshi Seo, Yukitoshi Motome, Takeo Kato
2007 Volume 76 Issue 1 Pages
013707
Published: January 15, 2007
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Phase transitions in 1/4-filled quasi-one-dimensional molecular conductors are studied theoretically on the basis of extended Hubbard chains including electron–lattice interactions coupled by interchain Coulomb repulsion. We apply the numerical quantum transfer-matrix method to an effective one-dimensional model, treating the interchain term within mean-field approximation. Finite-temperature properties are investigated for the charge ordering, the “dimer Mott” transition (bond dimerization), and the spin-Peierls transition (bond tetramerization). A coexistent state of charge order and bond dimerization exhibiting dielectricity is predicted in a certain parameter range, even when intrinsic dimerization is absent.
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Daisuke Tahara, Yukitoshi Motome, Masatoshi Imada
2007 Volume 76 Issue 1 Pages
013708
Published: January 15, 2007
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We study thermodynamic properties of an antiferromagnetic Ising model on the inverse perovskite lattice by using Monte Carlo simulations. The lattice structure is composed of corner-sharing octahedra and contains three-dimensional (3D) geometrical frustration in terms of magnetic interactions. The system with the nearest-neighbor interactions alone does not exhibit any phase transition, leading to a degenerate ground state with large residual entropy. The degeneracy is lifted by an external magnetic field or by an anisotropy in the interactions. Depending on the anisotropy, they stabilize either a 3D ferrimagnetic state or a partially-disordered antiferromagnetic (PDAF) state with a dimensionality reduction to 2D. By the degeneracy-lifting perturbations, all the transition temperatures of these different ordered states continuously grow from zero, leaving an unusual zero-temperature critical point at the unperturbed point. Such a zero-temperature multicriticality is not observed in other frustrated structures such as face-centered cubic and pyrochlore. The transition to the PDAF state is represented by either the first- or second-order boundaries separated by tricritical lines, whereas the PDAF phase shows 1/3 magnetization plateaus.
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Shinya Yoshioka, Eri Nakamura, Shuichi Kinoshita
2007 Volume 76 Issue 1 Pages
013801
Published: January 15, 2007
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Iridescence is observed in various kinds of animals that utilize optical interference phenomenon of microstructures to produce their brilliant colors. It appears according to the interference condition that relates the wavelength of the reflected light with the angle of view or incidence. However, the iridescence of the neck feather of rock dove looks very peculiar; the color change is limited only in two colors, green and purple, and the change occurs very suddenly by only slightly shifting the viewing angle. We show that this two-color iridescence originates from the surprisingly simple physical mechanism—thin-layer interference. The peculiarity lies in the fact that the higher-order interference condition is satisfied. This causes the sophisticated correspondence in the spectral line shape between the reflectance and the visual color sensitivities of human eye, and results in the two-color nature of the iridescence. It is also suggested that the rock dove’s vision perceives this two-color iridescence as a tool for visual signaling among rock doves.
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Kazuyuki Hara, Masato Okada
2007 Volume 76 Issue 1 Pages
014001
Published: January 15, 2007
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We propose a mutual learning with a latent teacher within the framework of on-line learning, and have analyzed its dynamical behavior through the statistical mechanics method. The proposed model consists of two learning steps: two students independently learn from a teacher, and then the students learn from each other through the mutual learning. A teacher is not used in the mutual learning, so we refer to the teacher as a latent teacher. Linear perceptrons are used as the teacher and student. Our analytical results show that the overlaps between teacher and students become larger through mutual learning. In addition, we found that the mutual learning converges into the bagging of the ensemble learning scheme. We also show that a student with a larger initial overlap for mutual learning transiently passes through a state of parallel boosting in the ensemble learning in the slow learning rate limit. We have concluded that mutual learning is able to mimic the integration mechanism of bagging and parallel boosting.
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Hiroyuki Nishimura, Akira Hamada
2007 Volume 76 Issue 1 Pages
014301
Published: January 15, 2007
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Total electron scattering cross sections for c-C
4F
8 have been measured in the energy range between 1 and 3000 eV using a compact linear-type electron transmission apparatus. Electrons scattered into a narrow forward angle were examined using some of the scattered currents and an empirical formula. The present results were compared with available theoretical and experimental data. Inelastic electron scattering cross sections were examined in the energy ranges of 1.5–7, 1.5–15, and 15–100 eV. The validity of the present results was examined. The most plausible electric dipole polarizability for c-C
4F
8 was chosen from the available data.
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Dae-Soung Kim, Young Soon Kim
2007 Volume 76 Issue 1 Pages
014302
Published: January 15, 2007
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Photoionization cross sections leading to the Al
2+ 3
l states from the
1S ground state of the Mg-like Al
+ have been calculated using the eigenchannel
R-matrix method. The calculations have been performed in
LS coupling using a configuration interaction for the target states as well as for the full atomic wave functions. The lower members of autoionizing Rydberg series converging to the Al
2+ 3
l thresholds are identified. The present calculations with good agreement between length and velocity gauges are compared with the available previous results of the Opacity Project and experimental measurements.
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Norihan Md. Arifin, Roslinda Md. Nazar, Norazak Senu
2007 Volume 76 Issue 1 Pages
014401
Published: January 15, 2007
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Feedback control was applied to the steady Marangoni–Bénard convection in a horizontal layer of fluid with a free-slip bottom heated from below and cooled from above. The critical values of the Marangoni numbers for the onset of steady convection are calculated and the latter is found to be critically dependent on the Crispation and Bond numbers. It is shown that the onset of instability can be delayed and the critical Marangoni number can be increased through the use of feedback control.
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Kazuo Yamada, Kazumasa Miyake, Shohei Kashiwamura
2007 Volume 76 Issue 1 Pages
014601
Published: January 15, 2007
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Two-fluid hydrodynamics is extended to three-fluid hydrodynamics including the “vortex fluid”, which denotes the system of vortex lines with the inertia mass of the vortex core. Characteristic constructions of hydrodynamics are considered in two typical configurations of vortex lines: one is the parallel vortex line configuration realized by rotating helium inside a cylinder, the other is the tangled configuration of vortex lines realized in turbulent pipe flow. Constitutional equations for three-fluid hydrodynamics are discussed for each configuration, including the equation of motion for momentum density proportional to the inertia mass of vortex fluid. By taking the vanishing limit of inertia mass, a condition is derived whereby the total force exerted on the vortex line vanishes, and the extent to which the three-fluid model approaches the two-fluid hydrodynamics in this limit are discussed.
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Masaaki Isobe, Mitsuko Onoda, Mitsuyuki Shizuya, Masahiko Tanaka, Eiji ...
2007 Volume 76 Issue 1 Pages
014602
Published: January 15, 2007
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We have studied the crystal structure of the new misfit-layer calcium cobaltite [2CaOH]
kCoO
2 (
k=0.576) by means of superspace-group formalism using synchrotron x-ray diffraction data. This compound is a kind of a composite crystal which consists of two interpenetrating subsystems: (a) [CoO
2]
∞ containing triangular lattices formed by edge-sharing CoO
6 octahedra and (b) [2CaOH]
∞ double-layered rock-salt-type slabs. The two subsystems have incommensurate periodicity along the
a-axis (
a1⁄
a2=
k=0.576), resulting in a modulated crystal structure due to the inter-subsystem interaction. It was found that the significant structural modulation is realized in the [2CaOH] subsystem. Modulation in the [CoO
2] subsystem is less marked than in the [2CaOH] ones owing to tight bonding of the closed-pack CoO
6 octahedra. Thick CoO
6 octahedra indicate insufficient hole-doping level in this compound.
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Kiyoshi Deguchi
2007 Volume 76 Issue 1 Pages
014603
Published: January 15, 2007
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The dielectric constant of pyridinium tetrafluoroborate C
5NH
6·BF
4 (PyBF
4) was measured in the frequency range of 300 Hz to about 10 MHz under pressures up to about 1.5 GPa. The critical slowing down of the dielectric relaxation was observed at all pressures examined, the relaxation frequency of which becomes lower with increasing pressure. The pressure derivative of the transition temperature
Tc1 between the paraelectric phase and the ferroelectric phase, (
dTc1⁄
dp)
0, is about 120 K/GPa. This is very large compared with those of other typical order-disorder ferroelectrics. The
p–
T phase diagram was discussed on the basis of phenomenological theory.
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Hiroaki Kajikawa, Shin Takahashi, Masaki Iwakoshi, Taiki Hoshino, Mako ...
2007 Volume 76 Issue 1 Pages
014604
Published: January 15, 2007
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We have measured the sound velocity,
v, and sound attenuation, α, in fluid selenium up to 1700 °C and 1666 bar including the semiconductor–metal (SC–M) transition region for the first time. The ultrasonic measurements were performed by an ultrasonic pulse transmission/echo method. A coherent phase-detection technique was used for a precise velocity measurement. Anomalous changes in the temperature dependence of
v were observed at pressures above 294 bar. The inflections of
v were closely related to the electronic properties and served as good indicators of the SC–M transition region except for the vicinity of the liquid–gas critical point.
v along isochores decreases with increasing temperature in the transition region, which means an increase in density fluctuations. Moreover, in addition to the critical attenuation, we also observed an anomalous increase in α in the transition region. The increase in α was attributed to an increase in bulk viscosity. On the basis of these results, we point out that a mesoscopic-scale inhomogeneity between semiconducting and metallic states exists in the transition region and induces slow structural relaxation.
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Nobuaki Shimoji, Kazunari Nakasone, Tomozo Tomoyose, Michisuke Kobayas ...
2007 Volume 76 Issue 1 Pages
014701
Published: January 15, 2007
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The DV-Xα method is applied in a study of the electronic states of α-AgI and α-CuBr by making use of the model cluster M
4X
15 (M=Ag, Cu; X=I, Br). By calculating the cation–cation distance dependence of the bond overlap population we have found that cation–anion bonding and cation–cation bonding are both covalent-like bonding, while anion–anion bonding is not covalent-like bonding. Especially, we have found that cation–anion bonding is strongly influenced by the cation–cation distance. From the result for the density of states, it has been comfirmed that the strength of the
p–
d hybridization between cation–
d and anion–
p orbitals is large for these orbitals in α-AgI and α-CuBr.
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Tetsuya Takeuchi, Takashi Yasuda, Masahiko Tsujino, Hiroaki Shishido, ...
2007 Volume 76 Issue 1 Pages
014702
Published: January 15, 2007
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Specific heat and de Haas–van Alphen (dHvA) measurements were performed on a high-quality single crystal of CePt
3Si without inversion symmetry in the tetragonal crystal structure. We observed distinct peaks in the specific heat
C at the superconducting transition temperature
Tc=0.46 K and the antiferromagnetic ordering temperature
TN=2.25 K, compared to the previous data, indicating an improvement of the sample quality. The temperature dependence of the electronic specific heat coefficient
Ce⁄
T below about 0.3 K is well described by the equation of
Ce⁄
T=γ
s+β
sT with γ
s=34.1 mJ/(K
2·mol) and β
s=1290 mJ/(K
3·mol), evidencing the existence of line nodes in the superconducting energy gap. Furthermore, the electronic specific heat coefficient γ
s in the superconducting state indicates a nonlinear magnetic field dependence γ
s(
H)∝\\sqrt
H, which also supports the presence of line nodes. We did not observe a discontinuous change of the Fermi surface at
PAF=0.6 GPa where the Néel temperature becomes zero, but observed a new dHvA branch above 1.5 GPa of which the cyclotron effective mass decreased steeply as a function of pressure from 19
m0 at 2.0 GPa to 11
m0 at 2.7 GPa.
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Yoshito Nonoyama, Akito Kobayashi, Yoshikazu Suzumura
2007 Volume 76 Issue 1 Pages
014703
Published: January 15, 2007
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The superconductivity in quasi-two-dimensional organic conductor α-(BEDT-TTF)
2NH
4Hg(SCN)
4, which occurs in the vicinity of charge density wave phase, has been investigated using the extended Hubbard model with both on-site repulsive interaction and nearest-neighbor repulsive interactions, and with the hopping energy estimated from the X-ray experiment. The pairing interactions induced by the spin and charge fluctuations are calculated in terms of the random phase approximation. The repulsive interactions are chosen so that the characteristic momentum of the charge fluctuation reproduces that of the X-ray diffuse scattering experiment. From the linearized gap equation, it is shown that the pairing for the singlet superconductivity is determined by the charge fluctuation. A good correspondence with the experiment is obtained for the pressure dependence of the superconducting transition temperature
Tc, which exhibits a maximum under uniaxial pressure.
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Hirotaka Manaka, Isao Yamada, Wataru Higemoto
2007 Volume 76 Issue 1 Pages
014704
Published: January 15, 2007
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Muon spin relaxation (μ
+SR) measurements were performed on a
S=1 of composite Haldane spin chains in IPA-CuCl
3, which consists of a spin-ladder network along the
a-axis. At a zero external magnetic field, the μ
+ spin relaxation became slightly faster with the development of a magnetic short-range order, but, as expected, oscillating spectra, which indicate a magnetic long-range order, did not appear. From the μ
+SR time spectra under transverse and longitudinal magnetic fields, fluctuation of the local field whose frequency was estimated to be 99±12 MHz was observed at 2.0 K, but it disappeared at 12 and 50 K. The appearance of the local field at a temperature between 12 and 2.0 K may suggest experimental evidence of the crossover from
S=1⁄2 spin state to
S=1 of composite Haldane spin state with decreasing temperature.
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Norio Akiyama, Shinji Muramatsu, Kentaro Ushio, Giuseppe Baldacchini
2007 Volume 76 Issue 1 Pages
014705
Published: January 15, 2007
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The Stark effect in absorption of the F
A center has been observed in KCl:Na. The changes of the absorption coefficient due to the applied electric field have been measured as a function of the photon energy. From these experimental data the energy difference between 2
px(y) and 2
s states has been evaluated.
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N. Tokuda, T. Nishioka, G. F. Chen, K. Deguchi, K. Kodama, N. K. Sato
2007 Volume 76 Issue 1 Pages
014706
Published: January 15, 2007
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We have measured dc magnetization
M(
H) of Ce
xLa
1−xRhIn
5 (
x=0.03, 0.05, and 0.1) to study a crystalline electric field (CEF) effect. We report that
M(
H) is isotropic at low temperatures in contrast to Ising like anisotropy in CeRhIn
5, yielding ground state wave functions similar to those of the parent compound CeIn
3. We also show that
M(
H) of
x=0.03, which exhibits the smallest intersite interactions, can be explained solely by the CEF effect, without taking into account the Kondo effect.
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Aya Yamamoto, Shinji Wada, Takeshi Matsumura
2007 Volume 76 Issue 1 Pages
014707
Published: January 15, 2007
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We report nuclear magnetic resonance (NMR) studies on evolutions of the spin fluctuation character in a divalent semiconductor TmTe with the applications of external magnetic field and pressure. Upon cooling below ∼20 K
125Te-resonance shift −Δ
H⁄
H in a high-field ∼7 T begins to deviate from the Curie–Weiss (CW) type increase at high temperatures, and exhibits a saturation behavior below ∼3–4 K. The nuclear spin–lattice relaxation rate
T1−1 changes the temperature dependence from the increasing behavior at high temperatures to a monotonic decrease below ∼35 K and to a rapid drop below ∼3–4 K, indicating successive freezing of different spin fluctuation modes. These NMR features lead to an interpretation that two distinct transitions take place in high-fields: from the paramagnetic state (state I) to an intermediate state (state II) below 20–35 K, and to a low temperature state (state III) below ∼3–4 K. The mechanism of the two successive transitions is discussed in terms of a possible octupolar order and an order of field-induced dipole or octupole moments of originally quadrupole moments of Tm
2+ ions, respectively, with the low-energy splitting of the crystal electric field levels. In a low-field ∼1 T, the negative Δ
H⁄
H continues the CW type increase down to ∼4 K. On the other hand,
T1−1 exhibits a pronounced increase below ∼15 K. These results indicate a development of the generalized susceptibility χ(
q) with the wave vector
q≠0 in low-fields, which could largely disturb the ordering in the state II. The application of a finite pressure of 0.9 GPa hardly changes the spin fluctuation character in low-fields, leading to a conjecture that the ferromagnetic order in the pressure-driven metallic state (
TC=14 K for ∼2.7 GPa) shares the basic mechanism with the ordering in the state II of the semiconducting state.
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Fumiko Yamada, Toshio Ono, Hidekazu Tanaka, Jun-ichi Yamaura
2007 Volume 76 Issue 1 Pages
014708
Published: January 15, 2007
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We report the single-crystal X-ray analysis and magnetic properties of a new double-layered perovskite antiferromagnet, Cs
3Cu
2Cl
4Br
3. This structure is composed of Cu
2Cl
4Br
3 double layers with elongated CuCl
4Br
2 octahedra and is closely related to the Sr
3Ti
2O
7 structure. An as-grown crystal has a singlet ground state with a large excitation gap of Δ⁄
kB\\simeq2000 K, due to the strong antiferromagnetic interaction between the two layers. Cs
3Cu
2Cl
4Br
3 undergoes a structural phase transition at
Ts\\simeq330 K accompanied by changes in the orbital configurations of Cu
2+ ions. Once a Cs
3Cu
2Cl
4Br
3 crystal is heated above
Ts, its magnetic susceptibility obeys the Curie–Weiss law with decreasing temperature even below
Ts and does not exhibit anomalies at
Ts. This implies that in the heated crystal, the orbital state of the high-temperature phase remains unchanged below
Ts, and thus, this orbital state is the metastable state. The structural phase transition at
Ts is characterized as an order–disorder transition of Cu
2+ orbitals.
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Yuki Fuseya, Masahisa Tsuchiizu, Yoshikazu Suzumura, Claude Bourbonnai ...
2007 Volume 76 Issue 1 Pages
014709
Published: January 15, 2007
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A role of interchain hopping in quasi-one-dimensional (Q-1D) electron systems is investigated by extending the Kadanoff–Wilson renormalization group of one-dimensional (1D) systems to Q-1D systems. This scheme is applied to the extended Hubbard model to calculate the temperature (
T) dependence of the magnetic susceptibility, χ(
T). The calculation is performed by taking into account not only the logarithmic Cooper and Peierls channels, but also the non-logarithmic Landau and finite momentum Cooper channels, which give relevant contributions to the uniform response at finite temperatures. It is shown that the interchain hopping,
t⊥, reduces χ(
T) at low temperatures, while it enhances χ(
T) at high temperatures. This notable
t⊥ dependence is ascribed to the fact that
t⊥ enhances the antiferromagnetic spin fluctuation at low temperatures, while it suppresses the 1D fluctuation at high temperatures. The result is at variance with the random-phase-approximation approach, which predicts an enhancement of χ(
T) by
t⊥ over the whole temperature range. The influence of both the long-range repulsion and the nesting deviations on χ(
T) is further investigated. We discuss the present results in connection with the data of χ(
T) in the (TMTTF)
2X and (TMTSF)
2X series of Q-1D organic conductors, and propose a theoretical prediction for the effect of pressure on magnetic susceptibility.
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Tomoya Kawai, Yusuke Okuda, Hiroaki Shishido, Arumugam Thamizhavel, Ta ...
2007 Volume 76 Issue 1 Pages
014710
Published: January 15, 2007
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We succeeded in growing a single crystal of CePtSi
3 with the tetragonal BaNiSn
3-type crystal structure by the Sn-flux method. CePtSi
3 is found to be an antiferromagnet with successive two transitions at
TN1=4.8 K and
TN2=2.4 K. The magnetization for
H||[100] indicates two metamagnetic transitions at
Hc1=1.8 kOe and
Hc2=15 kOe and saturates above
Hs=45 kOe, with an ordered moment of 1.15 μ
B/Ce. The [100] direction is an easy-axis in magnetization, while the [001] direction corresponds to a hard-axis. The anisotropy of the magnetic susceptibility and magnetization is very similar to that of pressure-induced superconductors of CeRhSi
3 and CeIrSi
3, which is commonly ascribed to the crystalline electric field effect.
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Tomonori Shirakawa, Satoshi Horiuchi, Yukinori Ohta, Hidetoshi Fukuyam ...
2007 Volume 76 Issue 1 Pages
014711
Published: January 15, 2007
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We consider superconductivity in boron (B) doped diamond using a simplified model for the valence band of diamond. We treat the effects of substitutional disorder of B ions by the coherent potential approximation (CPA) and those of the attractive force between holes by the ladder approximation under the assumption of instantaneous interaction with the Debye cutoff. We thereby calculate the quasiparticle life time, the evolution of the single-particle spectra due to doping, and the effect of disorder on the superconducting critical temperature
Tc. We in particular compare our results with those for supercell calculations to see the role of disorder, which turns out to be of crucial importance to
Tc.
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Dibyendu Mal, Suparna Sinha, Tapati Dutta, S. Mitra, Sujata Tarafdar
2007 Volume 76 Issue 1 Pages
014801
Published: January 15, 2007
Released on J-STAGE: August 12, 2010
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A study of crack patterns in laponite films of different thickness is presented. Two cracking regimes are observed. The earlier, with a higher rate of desiccation and shrinking, has predominantly 4-fold vertices in the crack network, while the later regime has less volume shrinking and forms mainly 3-fold vertices. The pattern shows a self-similarity under coarse-graining. The graph of the area covered by cracks versus minimum crack-width resolved, scales with the film thickness. Curves representing crack area for different thickness thus collapse onto a single curve.
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Ryota Takai, Kenji Nakayama, Wataru Saiki, Kiyokazu Ito, Hiromi Okamot ...
2007 Volume 76 Issue 1 Pages
014802
Published: January 15, 2007
Released on J-STAGE: August 12, 2010
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The effects of nonlinear resonances in a linear Paul trap have been investigated through systematic experiments and numerical simulations. The main causes of the nonlinearity that affects the stability of the ion motion are the use of circular (rather than hyperbolic) electrodes, their misalignments, and Coulomb interactions among the ions. A particle tracking code based on a two-dimensional model is employed to study the efficiency of plasma storage and to confirm the existence of nonlinear resonance stop bands. Experiments are performed with Ar
+ plasmas that are eventually detected by a Faraday cup after a short storage. The obtained data are compared with numerical simulations in which the exact three-dimensional structure of the trap system has been incorporated. Several nonlinear stop bands have been experimentally identified inside the Mathieu stability region. It is demonstrated that the location of a resonance stop band moves due to the space-charge potential depending on the number of confined ions.
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Takeshi Matsumura, Daisuke Okuyama, Youichi Murakami
2007 Volume 76 Issue 1 Pages
015001
Published: January 15, 2007
Released on J-STAGE: August 12, 2010
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Norikazu Todoroki
2007 Volume 76 Issue 1 Pages
015002
Published: January 15, 2007
Released on J-STAGE: August 12, 2010
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Takashi Ohnishi, Naoto Nagaosa
2007 Volume 76 Issue 1 Pages
015003
Published: January 15, 2007
Released on J-STAGE: August 12, 2010
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