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Daisuke Takahashi, Yusuke Kato
2009 Volume 78 Issue 2 Pages
023001
Published: February 15, 2009
Released on J-STAGE: December 28, 2011
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We derive the exact solution of low energy limit of Bogoliubov equations for excitations of Bose–Einstein condensate in the presence of arbitrary potential barrier and maximum current of condensate. Using this solution, we give the explicit expression for the transmission coefficient against the potential barrier, which shows partial transmission in the low energy limit. The wavefunctions of excitations in the low energy limit do not coincide with that of the condensate. The absence of the perfect transmission in the critical current state originates from local enhancement of density fluctuations around the potential barrier.
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Satoshi Yukawa, Takashi Shimada, Fumiko Ogushi, Nobuyasu Ito
2009 Volume 78 Issue 2 Pages
023002
Published: February 15, 2009
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A nonequilibrium distribution function of microscopic thermal current is studied by a direct numerical simulation in a thermal conducting steady state of particle systems. Two characteristic temperatures of the thermal current are investigated on the basis of the distribution. It is confirmed that the temperature depends on the current direction; Parallel temperature to the heat-flux is higher than antiparallel one. The difference between the parallel temperature and the antiparallel one is proportional to a macroscopic temperature gradient.
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Makio Uwaha, Hiroyasu Katsuno
2009 Volume 78 Issue 2 Pages
023601
Published: February 15, 2009
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It has been found that the simple grinding of crystals in a solution causes the conversion of the chiral structure of crystals and, in the case of organic molecules, the resultant conversion of molecular chirality. In order to clarify the mechanism of the chirality conversion, we study the change in the size distribution of chiral clusters in a Becker–Döring type model, in which chiral dimer reaction and grinding are implemented. In the absence of grinding, Ostwald ripening may cause chirality conversion if the initial size distribution is appropriate. With grinding crystals, the crystallization of chiral clusters causes an exponential amplification of the initial chiral imbalance resulting in a homochiral state. During chirality conversion, the total size distribution does not change.
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Kazumi Igawa, Hironari Okada, Kazunobu Arii, Hiroki Takahashi, Yoichi ...
2009 Volume 78 Issue 2 Pages
023701
Published: February 15, 2009
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Electrical resistivity and magnetic susceptibility measurements under high pressure were performed on an iron-based superconductor LaFePO. A steep increase in superconducting transition temperature (
Tc) of LaFePO with
dTc⁄
dP>4 K/GPa below
P=0.8 GPa was observed. These results are similar to isocrystalline LaFeAsO
1−xF
x system reported previously. X-ray diffraction measurements were also performed under high pressure up to 10 GPa, where linear compressibility κ
a and κ
c are presented.
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Yasuyuki Nakajima, Toshihiro Taen, Tsuyoshi Tamegai
2009 Volume 78 Issue 2 Pages
023702
Published: February 15, 2009
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We present the superconducting properties of single-crystalline Ba(Fe
0.9Co
0.1)
2As
2 by measuring its magnetization, resistivity, upper critical field, Hall coefficient, and magneto-optical images. The magnetization measurements reveal a fish-tail hysteresis loop at high temperatures and a relatively high critical current density above
Jc=10
5 A/cm
2 at low temperatures. The upper critical field determined by resistive transition is anisotropic with an anisotropic parameter of ∼3.5. Hall effect measurements indicate that Ba(Fe
0.9Co
0.1)
2As
2 is a multiband system and that the mobility of electrons is dominant. Magneto-optical imaging reveals a prominent Bean-like penetration of vortices, although there is a slight inhomogeneity in a sample. Moreover, we observe distinct superconductivity above 25 K, which leads us to speculate that a higher transition temperature can be realized by fine-tuning the Co-doping level.
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Yuki Fuseya, Toshikaze Kariyado, Masao Ogata
2009 Volume 78 Issue 2 Pages
023703
Published: February 15, 2009
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We study a microscopic mechanism of Fe-pnictide superconductor, considering the screening effects of Coulomb interaction in addition to the conventional spin-fluctuation mechanism. It is shown that, by electron doping, the transition temperature of superconductivity increases due to the “unscreening” effect even though the density of states decrease, while that of spin-density wave rapidly decreases due to breaking of nesting conditions. Our results give a clear interpretation to the mystery of photoemission spectroscopy and the nuclear relaxation rate observed in the Fe-pnictide superconductors.
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Takao Morinari, Takahiro Himura, Takami Tohyama
2009 Volume 78 Issue 2 Pages
023704
Published: February 15, 2009
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It is proposed that the presence of a tilted and anisotropic Dirac cone can be verified using the interlayer magnetoresistance in the layered Dirac fermion system, which is realized in quasi-two-dimensional organic compound α-(BEDT-TTF)
2I
3. Theoretical formula for the interlayer magnetoresistance is derived using the analytic Landau level wave functions and assuming local tunneling of electrons. It is shown that the resistivity as a function of the azimuthal angle of the magnetic field takes the maximum in the direction of the tilt if anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is described to determine the parameters of the tilt and anisotropy.
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Yutaka Itoh, Chishiro Michioka, Kazuyoshi Yoshimura, Kanako Nakajima, ...
2009 Volume 78 Issue 2 Pages
023705
Published: February 15, 2009
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We report on
7Li NMR studies of single crystals of the triangular-lattice Heisenberg antiferromagnet Li
7RuO
6. A slow critical divergence with a wide critical region of |
T⁄
TN−1|≤7 was observed in
7Li nuclear spin–lattice relaxation rate. The slowing down of staggered spin fluctuations was analyzed in a renormalized classical region of a two-dimensional triangular-lattice nonlinear sigma model. Spin stiffness constant was found to decrease to about 20% of its value in spin-wave approximation. The effect of spin frustration, e.g.,
Z2 vortex excitations on critical phenomena, is suggested.
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Daigorou Hirai, Tomohiro Takayama, Ryuji Higashinaka, Hiroko Aruga-Kat ...
2009 Volume 78 Issue 2 Pages
023706
Published: February 15, 2009
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Bulk superconductivity was discovered in BaRh
2P
2 (
Tc=1.0 K) and BaIr
2P
2 (
Tc=2.1 K), which are isostructural to (Ba,K)Fe
2As
2, indicative of the appearance of superconductivity over a wide variety of layered transition metal pnictides. The electronic specific heat coefficient γ in the normal state, 9.75 and 6.86 mJ/(mol K
2) for BaRh
2P
2 and BaIr
2P
2 respectively, indicate that the electronic density of states of these two compounds are moderately large but smaller than those of Fe pnictide superconductors. The Wilson ration
RW=χ⁄γ×π
2 kB2⁄3μ
B2 close to 1 indeed implies the absence of strong electron correlations and magnetic fluctuations unlike Fe pnictides.
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Masakazu Matsubara, Takeshi Ogasawara, Yasuhide Tomioka, Katsuhiro Tob ...
2009 Volume 78 Issue 2 Pages
023707
Published: February 15, 2009
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We report comparative studies of photoinduced spin and charge dynamics in the three kinds of the charge/orbital ordered (CO/OO) manganites. By the irradiation of a femtosecond laser pulse, ultrafast ferromagnetism is induced in Gd
0.55Sr
0.45MnO
3 by the photocarrier-induced double exchange interaction, while delayed ferromagnetism occurs in Nd
0.5Sr
0.5MnO
3 through the thermalizations of the spin and lattice sectors with the charge sector. In Pr
0.55(Ca
0.8Sr
0.2)
0.45MnO
3, neither of the ultrafast nor delayed ferromagnetism was observed. Such differences between photoinduced magnetisms will be discussed in terms of the lattice-structural change between the CO/OO and ferromagnetic states.
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Hiroshi Akera
2009 Volume 78 Issue 2 Pages
023708
Published: February 15, 2009
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Dynamics during the breakdown of the quantum Hall effect is studied theoretically in the Corbino geometry at a filling factor of 2. Spatio-temporal variations of the density of electrons in the first excited Landau level are calculated as well as those of the electron temperature. It is shown that the time constant of the population in this Landau level becomes quite long when the electron temperature is low compared to the Landau-level width.
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Kenichiro Tatsumi, Naoki Fujiwara, Hironari Okada, Hiroki Takahashi, Y ...
2009 Volume 78 Issue 2 Pages
023709
Published: February 15, 2009
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75As-nuclear magnetic resonance (NMR) on an iron (Fe)-based superconductor LaFeAsO
1−xF
x (
x=0.14) was performed under a pressure of 3 GPa. Enhancement of the superconducting transition temperature (
Tc) was confirmed from the relaxation rate (1⁄
T1);
Tc goes up to 40 K by applying pressure up to 3 GPa. 1⁄
T1T, which is temperature independent just above
Tc and gives a measure of the density of states (DOS) at the Fermi energy, enhances by applying pressure. These facts suggest that an increase of the DOS leads to the enhancement of
Tc. On the other hand, anomalous behavior of 1⁄
T1T observed at high temperatures is suppressed by applying pressure.
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Masatoshi Hiraishi, Ryosuke Kadono, Soshi Takeshita, Masanori Miyazaki ...
2009 Volume 78 Issue 2 Pages
023710
Published: February 15, 2009
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Superfluid density (
ns) in the mixed state of an iron pnictide superconductor Ba
1−xK
xFe
2As
2 is determined by muon spin rotation for a sample with optimal doping (
x=0.4). The temperature dependence of
ns is perfectly reproduced using the conventional BCS model for
s-wave paring, where the order parameter can be either a single-gap structure with Δ=8.35(6) meV [2Δ⁄
kBTc=5.09(4)] or double-gap structure with Δ
1=12 meV (fixed) [2Δ
1⁄
kBTc=7.3] and Δ
2=6.8(3) meV [2Δ
2⁄
kBTc=4.1(2)]. The latter is consistent with the recent result obtained by the angle-resolved photoemission spectroscopy. The large gap parameters (2Δ⁄
kBTc) indicate the extremely strong coupling of carriers to bosons that mediate the Cooper pairing.
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Jonathan P. L. Hatchett, Tatsuya Uezu
2009 Volume 78 Issue 2 Pages
024001
Published: February 15, 2009
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We study the dynamical nature of phase oscillator networks on a Bethe lattice. We derive self-consistent equations for the cavity fields (i.e. the oscillator probability distributions) by using the cavity method both in equilibrium and via an analytic approximation for non-equilibrium states. The order parameters and their evolution equations are obtained as functions of the cavity fields. The theoretical results and the accuracy of our approximations are confirmed by comparison with simulations involving direct integration of the Langevin equations describing the microscopic oscillator dynamics.
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Riki Kawashima, Hisashi Oochi, Hiroshi Isoda
2009 Volume 78 Issue 2 Pages
024002
Published: February 15, 2009
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Time series of ac conductivities at 2 kHz were measured along the direction perpendicular to the
c-axis of cerium nitrate crystal at temperatures from 200 to 11 K in three measuring processes of both cooling and heating cycles. Nonequilibrium nonlinear phenomena were observed above 120 K and below 190 K in the first cooling cycle. Anomalies were found in the probability distribution functions derived from the time series data. The limit cycle was observed in the phase portrait constructed from the data.
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Taichiro Takagi
2009 Volume 78 Issue 2 Pages
024003
Published: February 15, 2009
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Motivated by an attempt to develop a method for solving initial value problems in a class of one dimensional periodic cellular automata (CA) associated with crystal bases and soliton equations, we consider a generalization of a simple proposition in elementary mathematics. The original proposition says that any sequence of letters 1 and 2, having no less 1’s than 2’s, can be changed into a ballot sequence via cyclic shifts only. We generalize it to treat sequences of cells of common capacity
s>1, each of them containing consecutive 2’s (left) and 1’s (right), and show that these sequences can be changed into a ballot sequence via two manipulations, cyclic and “quasi-cyclic” shifts. The latter is a new CA rule and we find that various kink-like structures are traveling along the system like particles under the time evolution of this rule.
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Takeshi Yoshida
2009 Volume 78 Issue 2 Pages
024004
Published: February 15, 2009
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The diffusion processes of point vortex systems with no boundary are studied numerically and analytically. The mean square displacements in the radial direction are observed in equilibrium states corresponding to several parameters. It is shown that point vortex systems display an anomalous diffusion and that the mean square displacements exhibit a universal time dependence. The exponent of this time dependence corresponds to the results with circular boundary conditions reported by Kawahara and Nakanishi. On the other hand, the mean square displacement is dependent on system energy exponentially. The energy dependence of the mean square displacement is explained by the rough scaling theory. The probability distribution functions of the velocity field are also investigated numerically, and the results reinforce the theory of the dependence on system energy.
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Kazuhiro Deguchi, Michihiro Okuda, Atsushi Iwamae, Hiroaki Nakamura, K ...
2009 Volume 78 Issue 2 Pages
024301
Published: February 15, 2009
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We calculate optical near fields generated by a periodically structured 50-nm-wide slit array of a 50-nm-thick gold film with a finite difference time domain method. Efficiencies of the electric quadrupole (E2) and magnetic dipole (M1) transitions, which are associated with the space derivative of the excitation light field, are evaluated for the calculated optical fields. The E2 transition efficiency is largely enhanced in the case where the polarization of the incident light is perpendicular to the slit direction, while such an enhancement is not expected for the M1 transition for this polarization. The large enhancement of the E2 transition efficiency originates not only from the field enhancement but also from its localization near the slit edge. The slit period dependence of the enhancement of the E2 transition efficiency suggests the enhancement to be affected by surface plasmon resonance. In the case where the polarization of the incident light is parallel to the slit, a small enhancement is obtained for the E2 and M1 transitions, the value of which corresponds to (1⁄
k0d)
2, where
k0 is the wave number of the homogenously propagating light in vacuum and
d is the slit width.
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Kentaro Kanatani, Takeshi Ogasawara, Sadayoshi Toh
2009 Volume 78 Issue 2 Pages
024401
Published: February 15, 2009
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Properties of two equations describing the evolution of the probability density function of the relative dispersion in turbulent flow are compared by investigating their solutions: the self-similar telegraph equation derived by Ogasawara and Toh and the Richardson diffusion equation with the drift term. The solution of the self-similar telegraph equation vanishes at a finite point, while that of the Richardson equation extends infinitely just after the initial time. Each equation has a similarity solution, which is found to be an asymptotic solution of the initial value problem. The time lag has a dominant effect on the relaxation process into the similarity solution. The approaching time to the similarity solution can be reduced by advancing the time of the similarity solution appropriately. The Batchelor scaling is observed only for the telegraph case. The Richardson constant is estimated using the similarity solutions of both equations for our previous direct numerical simulation of two-dimensional free convection turbulence.
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Toshihiro Nakanishi, Kazuo Sakemi, Hirokazu Kobayashi, Kazuhiko Sugiya ...
2009 Volume 78 Issue 2 Pages
024402
Published: February 15, 2009
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We investigate a method to produce photon pairs by four-wave mixing in photonic crystal fibers (PCFs). By controlling the wavelength of the pump light, which determines the phase matching condition for four-wave mixing, we can obtain a broader spectrum of photon pairs than undesired Raman-scattered photons. We observe two-photon interference of photon pairs from a PCF with the help of an unbalanced Mach–Zehnder interferometer. Two-photon interference fringes with 83% visibility, which exceeds the classical limit of 50%, are obtained.
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Hidetsugu Sakaguchi, Kazutaka Noto
2009 Volume 78 Issue 2 Pages
024601
Published: February 15, 2009
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Viscous fingers in a channel with surface tension anisotropy are numerically studied. Scaling relations between the tip velocity
v, the tip radius ρ, and the pressure gradient
Px are investigated for two kinds of boundary conditions of pressure, when
v is sufficiently large. The power-law relations for the anisotropic viscous fingers are compared with two-dimensional dendritic growth. The exponents of the power-law relations are theoretically evaluated.
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Hironori Nakao, Jun Nishimura, Youichi Murakami, Akira Ohtomo, Tomoter ...
2009 Volume 78 Issue 2 Pages
024602
Published: February 15, 2009
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The crystal structure of [(LaMnO
3)
m(SrMnO
3)
m]
n artificial superlattices and the valence distribution of Mn ions have been studied using the X-ray scattering technique. The stacking structures were determined by the scattering intensities in the out-of-plane direction. The Mn valence distributions were evaluated by the energy dependence of the scattering intensity near the Mn K-edge, which was analyzed on the basis of the obtained crystal structures. The result indicates that the Mn valence becomes 3+ (4+) in the LaMnO
3 (SrMnO
3) layers, and the valence has an intermediate value between 3+ and 4+ only at the interface between LaMnO
3 and SrMnO
3 layers. We have also clarified that all the films are insulators independent of the periodicity
m.
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Shaoqing Wang
2009 Volume 78 Issue 2 Pages
024603
Published: February 15, 2009
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The thermal-expansion behaviors of zincblende GaP, GaAs, GaSb, BP, BAs, and BSb are comparatively studied by first-principles response-function calculation. In contrast to these gallium phases and the most of other III–V semiconductors, low-temperature negative thermal expansion is not found in the three borides. In order to explore the reason for the difference, the roles of the pressure-induced redistributions of the static and dynamic charges in the lattice-dynamic process of these phases are analyzed in details. Our study shows that the static charge moves towards the bond center and the dynamic effective charge decreases as a hydrostatic pressure is applied to these gallium phases, which leads to the reductions in their polarity and ionicity. However, both of the static and dynamic charges behave inversely in the three borides. As a result, these borides’ polarity and ionicity will increase under pressure. The fact suggests a correlation between polarity reduction and negative thermal expansion in III–V semiconductors.
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Masateru Takechi, Kazuo Ueda
2009 Volume 78 Issue 2 Pages
024604
Published: February 15, 2009
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Motivated by the discovery of superconductivity in β-pyrochlore oxides, we study property of rattling motion coupled with conduction electrons. We derive the general expression of the Green’s function of fully anharmonic lattice vibration within the accuracy of the second order perturbation of electron–ion interaction by introducing self-energy, vertex-correction, and normalization factor for each transition. Using the expression, we discuss the characteristic properties of the spectral function in the entire range from weakly anharmonic potential to double-well case, and calculate NMR relaxation rate due to the two phonon Raman process.
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Keisuke Shigetoh, Takahiro Onimaru, Akihiro Ishida, Motoko Akita, Kats ...
2009 Volume 78 Issue 2 Pages
024701
Published: February 15, 2009
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We report measurements of magnetization, magnetic susceptibility, specific heat, and neutron diffraction on a single crystal of the heavy fermion compound, Ce
4Ni
3Pb
4, crystallizing in a trigonal structure with two inequivalent Ce sites. In the paramagnetic state, the effect of crystal electric field (CEF) leads to the easy magnetization direction along the
c-axis. Magnetic Bragg peaks develop below
TN=3.0 K and are indexed with a propagation vector
k=[0,1,1⁄2]. Below
TN, a spontaneous moment of 10
−3 μ
B/Ce is observed only for
B⊥
c, while a metamagnetic transition is observed for
B||
c at 1.3 T. The small spontaneous moment in the
c-plane is ascribed to the slight canting of the antiferromagnetically aligned moments from the
c-axis. The inelastic neutron scattering spectrum is composed of four CEF excitations at 5.3, 19, 24, and 40 meV. The peaks at 19 and 40 meV have a rather large width of 10 meV, which is three times larger than that of the others. The wide peaks are assigned to excitations from the ground state of one Ce site, the Kondo temperature of which is higher than that of the Ce ions in the other site.
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Goro Oohata, Yuta Yokotsuji, DaeGwi Kim, Hajime Ishihara, Masaaki Naka ...
2009 Volume 78 Issue 2 Pages
024702
Published: February 15, 2009
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We have investigated the center-of-mass quantization effect on excitons in layered-compound PbI
2 ultra-thin films by precisely changing the layer thickness from 7 to 20 monolayers. Crystalline PbI
2 thin films that are fully oriented along the
c-axis were prepared by a vacuum deposition method. We confirmed that the surface roughness of the prepared thin films corresponds to one monolayer owing to the van der Waals interaction along the
c-axis peculiar to the layered compound, which is advantageous for the realization of the center-of-mass quantization effect. The optical spectra, such as absorption, transmittance, and reflectance clearly exhibit oscillatory structures originating from the quantized excitonic states with a quantum number of up to 15: the quantization energy amounts to ∼130 meV. From the analysis of the systematic results of the center-of-mass quantization, we experimentally determined the excitonic dispersion relation of PbI
2, which is well explained by a tight-binding exciton model instead of a usually used effective-mass model.
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Masayoshi Tange, Ryozo Yoshizaki
2009 Volume 78 Issue 2 Pages
024703
Published: February 15, 2009
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We investigate the dependence of the critical current density
Jc along the crystal
a-axis on the magnetic field along the
c-axis at high temperatures below the superconducting transition temperature in individual Bi
2Sr
2CaCu
2O
8+δ (Bi-2212) whiskers with surface barriers by electrical transport measurements.
Jc shows a low-field peak effect;
Jc increases with the magnetic field in a low-field region and shows a peak at the threshold field
Hpeak below 100 Oe. A comparison of the low-field peak effects in whiskers of different widths shows that
Hpeak depends on the sample width (i.e., the lateral dimension); the lateral axis is perpendicular to the magnetic field and the direction of current flow. A decrease in the sample width
w shifts
Hpeak toward a higher field. This systematic variation in
Hpeak with
w implies that the low-field peak effect observed in the Bi-2212 whiskers is associated with the effect of the finite
w on dilute vortices.
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Satoshi Higashitaniguchi, Makoto Seto, Shinji Kitao, Yasuhiro Kobayash ...
2009 Volume 78 Issue 2 Pages
024704
Published: February 15, 2009
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An
57Fe Mössbauer spectroscopic study of iron-based layered superconductors La
0.87Ca
0.13FePO and LaFeAsO
0.93F
0.07 under external magnetic fields of up to 14 T was performed. Our results suggest that hyperfine fields induced by local magnetic moments are, if any, small and that the magnetic feature of Fe in La
0.87Ca
0.13FePO and LaFeAsO
0.93F
0.07 is most likely to be paramagnetism with itinerant electrons. This feature is confirmed both above and below the transition temperature for LaFeAsO
0.93F
0.07. Furthermore, the temperature dependence of the iron-specific phonon density of states in La
0.87Ca
0.13FePO was measured by using the nuclear resonant inelastic scattering of synchrotron radiation. We have found that the temperature-dependent change in the iron-specific phonon density of states of La
0.87Ca
0.13FePO was smaller than that of LaFeAsO
0.89F
0.11.
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Yositake Takane
2009 Volume 78 Issue 2 Pages
024705
Published: February 15, 2009
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We theoretically study nonequilibrium spin transport in a superconducting wire connected by tunnel junctions to two ferromagnetic metal wires, each of which serves as an injector or detector of spin-polarized electron current. We present a set of Boltzmann equations to determine nonequilibrium quasiparticle distributions in this system, and obtain an analytical expression for the nonlocal spin signal in the case of small injection current. It is shown that the quasiparticle distribution in the ferromagnetic metal for detection strongly affects the magnitude of the spin signal. At low temperatures, since nonequilibrium quasiparticles created by the tunneling from the superconductor dominate thermally excited ones, the spin signal becomes independent of temperature. This explains the convergence of the spin signal with decreasing temperature observed in a recent experiment by Poli
et al.
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Soutarou Tanaka, Nobuhiro Shimazui, Hiroshi Takatsu, Shingo Yonezawa, ...
2009 Volume 78 Issue 2 Pages
024706
Published: February 15, 2009
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We synthesized
ACu
3Ru
4O
12 (
A=Na, Na
0.5Ca
0.5, Ca, Ca
0.5La
0.5, La) and measured their DC magnetization, AC susceptibility, specific heat, and resistivity, in order to investigate the effects of the hetero-valent substitution. A broad peak in the DC magnetization around 200 K was observed
only in CaCu
3Ru
4O
12, suggesting the Kondo effect due to localized Cu
2+ ions. However, the electronic specific heat coefficients γ exhibit large values not only for CaCu
3Ru
4O
12 but also for all the other samples. Moreover, the Wilson ratio and the Kadowaki–Woods ratio of our samples are all similar to the values of other heavy-fermion compounds. These results question the Kondo effect as the dominant origin of the mass enhancement, and rather indicate the importance of correlations among itinerant Ru electrons.
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Shinji Michimura, Akira Shigekawa, Fumitoshi Iga, Toshiro Takabatake, ...
2009 Volume 78 Issue 2 Pages
024707
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Powder neutron diffraction analysis was performed on Tm
11B
4, which undergoes successive transitions at
TN1=11.7 K,
T*=11 K, and
TN2=10 K. An incommensurate structure with two propagation vectors,
k2=[1±
k′±
k″,±
k″,0] and
k2′=[1±
k′±3
k″,±
k″,0] (
k′=0.1226 and
k″\\simeq0.012), is suggested for phase II (
T*≤
T≤
TN1). Phase III (
TN2≤
T≤
T*) is described by one propagation vector,
k3=[1±
k′,0,0]. The propagation vector for phase IV (
T≤
TN2) further changes to a commensurate one characterized by
k4=[100]. Four Tm moments in the
c-plane order in a (+−+−) type, where + and − mean the directions of the moments parallel and antiparallel to the
c-direction, respectively. The diffuse scattering intensity around the (100) magnetic reflection remains above
TN2 up to 20 K.
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Masahiro Oshita, Satoshi Yotsuhashi, Hideaki Adachi, Hisazumi Akai
2009 Volume 78 Issue 2 Pages
024708
Published: February 15, 2009
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We present a calculation of Seebeck coefficient derived by Kubo–Greenwood formula with the density functional theory. The electronic structure calculation being the Korringa–Kohn–Rsestoker Green’s function method with coherent potential approximation and local density functional method (KKR-CPA-LDA). We show the results for transition metals and metal alloys. In particular, the result for palladium-silver alloy shows good agreement with the experimental data. This calculation shows that the role of mean free time associated to each orbital is quite important to obtain an accurate result of the Seebeck coefficient.
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Tian Qian, Kosuke Nakayama, Yujie Sun, Toshiyuki Arakane, Takafumi Sat ...
2009 Volume 78 Issue 2 Pages
024709
Published: February 15, 2009
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We report high-resolution photoemission spectroscopy (PES) of quasi one-dimensional (1D) metal NaV
2O
4. We found that the valence band consists of well-separated two main bands; one originates in the V 3
d states located around the Fermi level (
EF) and the other is due to the O 2
p states situated far away from
EF in qualitatively good agreement with the band calculation. The PES spectrum near
EF shows a power-law behavior characteristic of quasi-1D materials. The anomalous exponent α shows a considerable temperature dependence, in particular around the magnetic transition temperature. The temperature dependence of α is also consistent with the variation of the transport anisotropy with temperature. These results suggest a close relationship between the electronic structure near
EF and the magnetic order and/or the dimensional crossover.
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Nam Lyong Kang, Sang Don Choi
2009 Volume 78 Issue 2 Pages
024710
Published: February 15, 2009
Released on J-STAGE: December 28, 2011
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Utilizing the optical transition formula derived by a projection method on the linear response scheme, we obtain the optical transition linewidths for the electron system in square well due to piezoelectric phonon scattering in CdS and ZnS. We find that the widths increase with the temperature, but decrease as the well width increases for both materials. We also find that the widths decrease as the electron density increases, and the widths in CdS are larger than those in ZnS since the average electromechanical coupling constant is larger.
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Yusaku Horita, Yoshiyuki Ono
2009 Volume 78 Issue 2 Pages
024711
Published: February 15, 2009
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In order to study the stability of the multimode Peierls (MMP) state in the θ-type lattice system, the stable state is studied using a modified square-lattice Su–Schrieffer–Heeger (SSH) model. Since the MMP state has been predicted for the 2D square-lattice system with the SSH type electron–lattice (e–l) interaction and with a half-filled electronic band, we study the lowest energy state in the system, mimicking the θ-type lattice structure, where the transfer integral in one of the diagonal directions is added. The MMP state has the lattice distortions not only with the nesting vector
Q but also with many others parallel to
Q, and there are many degenerate states in the case of the 2D square-lattice electronic system. It is found that the energy of the MMP state decreases by increasing the transfer integral in the diagonal direction, and the amount of the decrease depends on the pattern of the lattice distortions. Consequently, the degeneracy of the MMP state is removed. This phenomenon is peculiar to the MMP state and does not occur in the single-mode Peierls (SMP) state which has only the
Q-mode distortion and the energy of which is almost independent of the electronic transfer in the diagonal direction. When this transfer integral is non-zero but sufficiently samll compared to those in the vertical and horizontal directions, the lowest energy state is the MMP state that has the lattice distortions with wave vectors
Q and
Q⁄2. We discuss the reason why this state is chosen.
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Nguyen D. Dung, Yuuki Ota, Kiyohiro Sugiyama, Tatsuma D. Matsuda, Yosh ...
2009 Volume 78 Issue 2 Pages
024712
Published: February 15, 2009
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A series of ternary compounds RCu
2Si
2 (R: rare earth) has been grown in single-crystalline form by the flux method. The magnetic properties of these compounds were investigated by measuring the lattice parameter, electrical resistivity, magnetic susceptibility, and magnetization. All the compounds crystallize in the tetragonal ThCr
2Si
2-type structure. Most of these compounds order antiferromagnetically at low temperatures, except when R=Y, La, Yb, and Lu. The magnetic anisotropy in the susceptibility and magnetization at low temperatures is found to be relatively small despite the tetragonal crystal structure. An increase in the electrical resistivity just below the ordering temperature and a first-order-like transition are characteristic features of RCu
2Si
2 with R = light rare earth and R = heavy rare earth, respectively.
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Yuta Otsuka, Masaru Tsukada
2009 Volume 78 Issue 2 Pages
024713
Published: February 15, 2009
Released on J-STAGE: December 28, 2011
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The crystal structures of several polyacene and pentacene derivatives are theoretically calculated by the mm3 molecular field method and the first-principles density functional calculation. The relation between the crystal structure and the energy band for these systems is analyzed in detail. In polyacene, two major structural changes with the degree of polymerization are found and their effect on the energy band is elucidated. The size and shape of the substituent groups to pentacene have a strong effect on the molecular arrangement in the crystal, in particular, on the stacking of the acene π-planes between the adjacent molecules. From the viewpoint of high mobility, we found promising crystal energy band features for a pentacene derivative with 6,13-triethylsilylpentacene as a substituent group.
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Fumiaki Sawano, Tomohiro Suko, Taichi S. Inada, Shuichi Tasaki, Ichiro ...
2009 Volume 78 Issue 2 Pages
024714
Published: February 15, 2009
Released on J-STAGE: December 28, 2011
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We have measured and analyzed the resistivity and voltage–current characteristics of the charge-ordered organic salt θ-(BEDT-TTF)
2Cs
M(SCN)
4 (
M=Zn, Co, and Co
0.7Zn
0.3). At 4.3 K, all the samples show giant nonlinear conduction, in which the
c-axis resistivity markedly decreases with external current by a factor of 10 against a small electric field of 1 V/cm. The temperature dependence of the resistivity is well described by an activation law, the activation energy of which is evaluated to be 2 meV in the low-current limit, and linearly decreases with external current. The activation energy and x-ray intensity near
q2=(0,
k,1⁄2) are found to show the same dependence on current density. This coincidence strongly suggests that the energy gap of the charge order indexed by
q2 is an order parameter of this phenomenon.
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Hiroshi Watanabe, Masao Ogata
2009 Volume 78 Issue 2 Pages
024715
Published: February 15, 2009
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We study the ground state properties of a periodic Anderson model in a two-dimensional square lattice with a variational Monte Carlo method. It is shown that there are two different types of quantum phase transition: a conventional antiferromagnetic transition and a Fermi-surface reconstruction that accompanies a change in the topology of the Fermi surface. The former is induced by the simple back-folding of the Fermi surface, while the latter is induced by the localization of
f electrons. The mechanism of these transitions and its relationship with the results of recent experiments on the Fermi surface are discussed in detail.
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Terutaka Goto, Tomoyuki Watanabe, Seiji Tsuduku, Haruki Kobayashi, Yui ...
2009 Volume 78 Issue 2 Pages
024716
Published: February 15, 2009
Released on J-STAGE: December 28, 2011
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Low-temperature elastic properties of the clathrate compound Ce
3Pd
20Si
6 were investigated using ultrasonic measurements. Pronounced softening of elastic constants (
C11−
C12)⁄2 and
C44 with decreasing temperature indicates a precursor of electric quadrupole ordering due to a Γ
8 quartet ground sate with an orbital degeneracy for 8c site of a Ce ion. A minimum of (
C11−
C12)⁄2 at
TC=170 mK indicates a transition from paramagnetic phase I to an ordered phase III. Applied magnetic fields induce an antiferro-quadrupole (AFQ) ordered phase II with highly anisotropic character depending on the field direction, which resembles the AFQ phase with
Oxy-type order parameter in CeB
6 with the Γ
8 ground sate. The order paramater of the phase III may be characterized by either magnetic dipole or magnetic octupole. The Γ
7 ground state at 4a site may fall into a singlet screened by conduction electrons at low temperatures without long-range magnetic ordering.
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Kazumi Igawa, Hironari Okada, Hiroki Takahashi, Satoru Matsuishi, Yoic ...
2009 Volume 78 Issue 2 Pages
025001
Published: February 15, 2009
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Tadashi Adachi, Hidetaka Sato, Masaki Fujita, Kazuyoshi Yamada, Yoji K ...
2009 Volume 78 Issue 2 Pages
025002
Published: February 15, 2009
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Atsushi Harada, Nobukatsu Tamura, Hidekazu Mukuda, Yoshio Kitaoka, Kou ...
2009 Volume 78 Issue 2 Pages
025003
Published: February 15, 2009
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Sota Tsukada, Akiko Masaki, Hiroyuki Mori
2009 Volume 78 Issue 2 Pages
025004
Published: February 15, 2009
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Isao Watanabe, Tadashi Adachi, Satoshi Yairi, Yoji Koike, Kanetada Nag ...
2009 Volume 78 Issue 2 Pages
028001
Published: February 15, 2009
Released on J-STAGE: December 28, 2011
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