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Yoshio Kuramoto, Hiroaki Kusunose, Annamária Kiss
2009 Volume 78 Issue 7 Pages
072001
Published: July 15, 2009
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In this paper we review experimental and theoretical results on higher electronic multipoles in solids with strong correlations. Recent experiments and their theoretical interpretation have confirmed the ordering of octupoles and even higher multipoles in rare-earth and actinide compounds with
f electrons. The concept of multipoles is critically examined in point groups where spherical tensors of different ranks mix. Using a phenomenological approach, we demonstrate how linear and nonlinear couplings of different multipoles lead to rich phase diagrams and anomalies in physical observables. As actual representative systems, we first consider Ce
xLa
1−xB
6, for which resonant X-ray scattering probed the octupole order for the first time, and NpO
2, where quadrupoles induced by the octupole order have been observed. We then consider a class of compounds called skutterudites as the most convenient system for systematic study. Particular emphasis is placed on the ordering of scalar components from fourth-rank tensors (hexadecapoles) and sixth-rank tensors (hexacontatetrapoles). A comparison of a skutterudite PrFe
4P
12 and URu
2Si
2 is made, where much fewer carriers remain in the ordered states than in the disordered phase. The even number (two) of
f electrons per site in Pr
3+ or U
4+ makes the system free from the Kramers degeneracy, in contrast to standard models for Mott transitions. Hence, it is pointed out that multipole orders, particularly the scalar order, should provide a new route for studying the dichotomy between the itinerant and localized behaviors of electrons.
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Hiromasa Tamaki, Kazumasa Miyake, Yoji Ohashi
2009 Volume 78 Issue 7 Pages
073001
Published: July 15, 2009
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We investigate the possibility of an unconventional spin density wave (SDW) in the attractive Hubbard model with finite spin polarization. We show that pairing and density fluctuations induce a transverse
d-wave SDW near the half-filling. This novel SDW is related to the
d-wave superfluidity induced by antiferromagnetic spin fluctuations, in the sense that they are connected with each other through Shiba’s attraction–repulsion transformation. Our results predict the
d-wave SDW in real systems, such as cold Fermi atom gases with a population imbalance and compounds involving valence skipper elements.
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Takaaki Kawamura, Peter A. Maksym
2009 Volume 78 Issue 7 Pages
073601
Published: July 15, 2009
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Using RHEED wave functions calculated on the basis of multiple scattering theory, one of the possible origins of RHEED intensity oscillation during growth is studied. This origin is the varying surface atomic row density which affects the interference of waves reflected from the surface. As an example, the specular beam intensity and the wave function are calculated for Si(001) surfaces with various atomic row densities.
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Koshi Takenaka, Ryotaro Watanabe, Hiroomi Yamada, Masao Tabuchi, Yoshi ...
2009 Volume 78 Issue 7 Pages
073701
Published: July 15, 2009
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The effect of disorder on the transition temperature
Tc of the oxypnictide superconductor
LnFeAsO
1−xF
x is explored. Disorder is controlled by ionic-radius mismatch of the
Ln-site elements with the doped carrier density kept constant. The x-ray diffraction and x-ray absorption fine structure experiments confirmed that the averaged lattice parameters and the local fluctuation of the Fe–As bond length are identical but, nevertheless,
Tc decreases in the order of
Ln=Nd, Ce
0.62Gd
0.38, and La
0.62Dy
0.38. This type of weak disorder reduces
Tc possibly via local fluctuation of the Fe–As bond angle.
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Akari Takayama, Seigo Souma, Takafumi Sato, Toshiyuki Arakane, Takashi ...
2009 Volume 78 Issue 7 Pages
073702
Published: July 15, 2009
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We have performed low-energy ultrahigh-resolution angle-resolved photoemission spectroscopy on CeSb to elucidate the bulk electronic structure responsible for the magnetic phase transition. By using a newly developed xenon-plasma discharge lamp, we clearly observed the splitting of Sb 5
p3⁄2 and Ce 5
d bands near the Fermi level as well as their strong hybridization below the Néel temperature (
TN=16 K). We also revealed distinct differences in the band structure between the antiferropara- and antiferro-magnetic phases. These experimental results are discussed in terms of the
p–
f/
p–
d mixing effect, the exchange splitting, and the magnetic band-folding. The present result also explains the emergence of fine structures in the optical conductivity in the magnetic phase.
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Naofumi Aso, Kiwamu Ishii, Hideki Yoshizawa, Tetsuya Fujiwara, Yoshiya ...
2009 Volume 78 Issue 7 Pages
073703
Published: July 15, 2009
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Magnetic neutron diffraction measurements were carried out on the heavy-fermion antiferromagnet CeRhIn
5 under hydrostatic pressure. The incommensurate (IC) magnetic ordering is known to be characterized by the propagation vector
τ=(0.5,0.5,±δ). We have found that when the temperature is lowered at
P∼1.48 GPa, the magnetic Bragg peak with δ=0.326 rapidly disappears and instead a new Bragg peak with δ=0.391 suddenly emerges at a temperature close to the superconducting transition temperature. This suggests the possibility that the antiferromagnetic order is affected by the superconductivity.
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Yoshiaki Kobayashi, Ayaka Kawabata, Sang Chul Lee, Taketo Moyoshi, Mas ...
2009 Volume 78 Issue 7 Pages
073704
Published: July 15, 2009
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NMR longitudinal relaxation rates 1⁄
T1 and Knight shifts
K have been measured for superconducting samples of LaFe
1−yCo
yAsO
1−xF
x with
y=0.0 and 0.0075 and for a nonsuperconducting metallic sample with
y=0.1, where the
x values are fixed at 0.11. The temperature (
T) dependence of 1⁄
T1 below the superconducting transition temperature
Tc has been found to be markedly different from the behavior 1⁄
T1∝
T2.5–3.0 reported by many groups in the entire
T range measured [(0.1–0.2)
Tc<
T<
Tc]. The nonexistence of the coherence peak has also been found. On the basis of the results of the measurements and other kinds of existing data, arguments are presented on the superconducting symmetry of the Fe pnictide systems, where the several points that cannot be easily explained by existing theories, are pointed out. Results of the measurements on the nonsuperconducting metallic samples are also presented.
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Yo Machida, Kosuke Tomokuni, Takayuki Isono, Koichi Izawa, Yasuyuki Na ...
2009 Volume 78 Issue 7 Pages
073705
Published: July 15, 2009
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Thermal transport measurements have been performed on single-crystalline Co-doped BaFe
2As
2 down to 0.1 K and under magnetic fields up to 7 T. Significant peak anomalies are observed in both thermal conductivity and thermal Hall conductivity below
Tc as an indication of the enhancement of the quasiparticle mean-free path. Moreover, we find a sizable residual
T-linear term in thermal conductivity, possibly due to a finite quasiparticle density of states in the superconducting gap induced by impurity pair breaking. Our findings support a pairing symmetry compatible with the theoretically predicted sign-reversing
s-wave state.
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Kazuyuki Matsubayashi, Naoyuki Katayama, Kenya Ohgushi, Atsushi Yamada ...
2009 Volume 78 Issue 7 Pages
073706
Published: July 15, 2009
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We measured the electrical resistivity and ac magnetic susceptibility of BaFe
2As
2 and SrFe
2As
2 single crystals under pressure using a cubic anvil apparatus. For BaFe
2As
2, the antiferromagnetic (AF) and structural transitions are suppressed with increasing pressure. Unexpectedly, these transitions persist up to 8 GPa, and no signature of a superconducting transition was observed in the pressure range investigated here. On the other hand, the AF and structural transitions of SrFe
2As
2 collapse at around the critical pressure
PC∼5 GPa, resulting in the appearance of bulk superconductivity. The superconducting volume fraction abruptly increases above
PC, and shows a dome centered at approximately 6 GPa. Our results suggest that the bulk superconducting phase competes with the AF/orthorhombic phase and only appears in the narrow pressure region of the tetragonal phase.
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Takashi Hotta
2009 Volume 78 Issue 7 Pages
073707
Published: July 15, 2009
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In an electron system coupled with anharmonic phonons, i.e.,
rattling, inverse isotope effect on the Kondo temperature
TK is found to occur by the numerical evaluation of the Sommerfeld constant γ of the Anderson–Holstein model. For the anharmonic potential of an oscillator with mass
M in which large γ has been found to be almost independent of an applied magnetic field, γ is significantly suppressed when
M is increased, i.e.,
TK is enhanced due to the relation of γ∼
TK−1 in the Kondo problem, leading to the inverse isotope effect on
TK. Since this phenomenon does not occur for harmonic phonons, it can be a key experiment to prove the relevance of rattling to magnetically robust heavy electron state.
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Naoki Kase, Jun Akimitsu, Yasuyuki Ishii, Takao Suzuki, Isao Watanabe, ...
2009 Volume 78 Issue 7 Pages
073708
Published: July 15, 2009
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We report here the magnetic properties of the thulium-based reentrant superconductor Tm
5Rh
6Sn
18 (
Tc=2.2 K), which were determined by magnetization and μSR measurements. The spontaneous oscillation signal in the μSR spectra gradually develops under zero magnetic field below 13 K. The development of a quasi-static local magnetic field is also observed even below
Tc, indicating the coexistence of magnetism and superconductivity at zero magnetic field. From the analysis of longitudinal μSR measurements, magnetic ordering can be considered to be not truly long range but superparamagnetic.
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Naoyuki Sanada, Ryuta Watanuki, Kazuya Suzuki, Mitsuhiro Akatsu, Toshi ...
2009 Volume 78 Issue 7 Pages
073709
Published: July 15, 2009
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We grew single crystals of TbCoGa
5 and measured their magnetic susceptibility, specific heat, and elastic constants. The result of the magnetic susceptibility measurement suggests that the
c- and
ab-components of the magnetic moments of Tb
3+ ions order independently at
TN1=36.2 K and
TN2=5.4 K, respectively. The magnetic entropy change indicates that the degeneracy of internal degrees of freedom is not fully lifted in the intermediate phase. In addition, the degeneracy of electric-quadrupolar (orbital) degrees of freedom exists in spite of the formation of magnetic order because the elastic constants show softening in the intermediate phase. It is considered that the magnetic ordering of the
ab-component is suppressed by the existence of the degeneracy of quadrupolar degrees of freedom in TbCoGa
5.
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Mikio Eto, Tomohiro Yokoyama
2009 Volume 78 Issue 7 Pages
073710
Published: July 15, 2009
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We theoretically investigate the extrinsic spin Hall effect (SHE) in semiconductor heterostructures, caused by scattering at an artificial potential created by an antidot, STM tip, etc. The potential is electrically tunable. First, we formulate the SHE in terms of phase shifts in the partial wave expansion for a two-dimensional electron gas. The effect is significantly enhanced by resonant scattering when the attractive potential is properly tuned. Second, we examine a three-terminal device including an antidot, which possibly produces a spin current with a polarization of more than 50%.
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Masashi Fujii, Akinori Awazu, Hiraku Nishimori
2009 Volume 78 Issue 7 Pages
073801
Published: July 15, 2009
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Quasi-one-dimensional bidirectional particle flow including the effect of chemotaxis is investigated through a modification of the John–Schadschneider–Chowdhury–Nishinari model. Specifically, we permit multiple lanes to be shared by both directionally traveling particles. The relation between particle density and flux is studied for several evaporation rates of pheromone, and the following results are obtained: i) in the low-particle-density range, the flux is enlarged by pheromone if the pheromone evaporation rate is sufficiently low, ii) in the high particle-density range, the flux is largest at a reasonably high evaporation rate and, iii) if the evaporation rate is at the level intermediate between the above two cases, the flux is kept small in the entire range of particle densities. The mechanism of these behaviors is investigated by observing the spatiotemporal evolution of particles and the average cluster size in the system.
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Midori Tanaka, Yoshitaka Tanimura
2009 Volume 78 Issue 7 Pages
073802
Published: July 15, 2009
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A multistate displaced oscillator system strongly coupled to a heat bath is considered a model of an electron transfer (ET) reaction system. By performing canonical transformation, the model can be reduced to the multistate system coupled to the Brownian heat bath defined by a non-ohmic spectral distribution. For this system, we have derived the hierarchy equations of motion for a reduced density operator that can deal with any strength of the system bath coupling at any temperature. The present formalism is an extension of the hierarchy formalism for a two-state ET system introduced by Tanimura and Mukamel into a low temperature and multistate system. Its ability to handle a multistate system allows us to study a variety of problems in ET and nonlinear optical spectroscopy. To demonstrate the formalism, the time-dependent ET reaction rates for a three-state system are calculated for different energy gaps.
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Yoshihiro Yamazaki, Hiroki Yoshino, Machiko Izui, Yukiko Sato, Mitsugu ...
2009 Volume 78 Issue 7 Pages
074001
Published: July 15, 2009
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Humidity–temperature conditions for the emergence of various domain patterns of ascorbic acid crystal are identified, where the crystal grows from its thinly spreading aqueous solution by solvent evaporation. In particular, under a low-humidity condition, the coexistent pattern is formed by two domains having different growth rates. In the faster growing domain, there exists a clear time delay between the crystal growth in the solution and the drying of the crystal surface. From the shape of the domain boundary in the coexistent pattern, the growth rate ratio between the two domains can be estimated.
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Rei Tatsumi, Yosuke Yoshimura
2009 Volume 78 Issue 7 Pages
074002
Published: July 15, 2009
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Solvophobic effects on an infinitely-thin hard needle by a solvent–solvent attractive interaction through a square-well potential are studied for the three-dimensional system. The expansion of the chemical potential with respect to needle length
L indicates that the solvophobic effects on an extremely short needle are proportional to
L3, which is
L5⁄2 in the two-dimensional system. The solvophobic effects on a needle of finite length are evaluated by a Monte Carlo calculation of a free-path distribution of a light point particle in a square-well fluid. Solvophobic solvation is exothermic at low solvent densities and endothermic at high solvent densities. Solvophobic interaction can be attractive or repulsive depending on the configuration of the interacting hard needles as well as on solvent density. The solvophobic effects in the three-dimensional system are qualitatively the same as those in the two-dimensional system. Several differences between the three- and two-dimensional systems are discussed.
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Takanori Sugihara, Junichi Higo, Haruki Nakamura
2009 Volume 78 Issue 7 Pages
074003
Published: July 15, 2009
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We develop a simple algorithm to parallelize generation processes of Markov chains. In this algorithm, multiple Markov chains are generated in parallel and jointed together to make a longer Markov chain. The joints between the constituent Markov chains are processed using the detailed balance. We apply the parallelization algorithm to multicanonical calculations of the two-dimensional Ising model and demonstrate accurate estimation of multicanonical weights.
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Hiroyuki Kobayashi, Yoshiyuki Fukumoto, Akihide Oguchi
2009 Volume 78 Issue 7 Pages
074004
Published: July 15, 2009
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A frustrated Ising model on a diamond hierarchical lattice is studied. We obtain the exact partition function of this model and calculate the transition temperature, specific heat, entropy, magnetization, and ferromagnetic correlation function. Depending on the magnitude of a parameter giving the frustration, there exist three types of ground states: ferromagnetic, classical spin-liquid with highly developed short-range order, and paramagnetic. The dependence of the zero-temperature entropy on the frustration parameter has an infinite number of steps. The temperature dependence of the specific heat exhibits many peaks with decreasing temperature and entropy loss. The dominant spin configurations at low temperatures are also specified.
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Rie Tokita, Takaki Katoh, Yusuke Maeda, Jun-ichi Wakita, Masaki Sano, ...
2009 Volume 78 Issue 7 Pages
074005
Published: July 15, 2009
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We have studied the morphological diversity and change in bacterial colonies, using the bacterial species
Escherichia coli, as a function of both agar concentration
Ca and nutrient concentration
Cn. We observed various colony patterns, classified them into four types by pattern characteristics and established a morphological diagram by dividing it into four regions. They are regions A [diffusion-limited aggregation (DLA)-like], B (Eden-like), C (concentric-ring), and D (fluid-spreading). In particular, we have observed a concentric-ring colony growth for
E. coli. We focused on the periodic growth in region C and obtained the following results: (i) A colony grows cyclically with the growing front repeating an advance (migration phase) and a momentary rest (consolidation phase) alternately. (ii) The growth width
L and the bulge width
W in one cycle decrease asymptotically to certain values, when
Ca is increased. (iii)
L does not depend on
Cn, while
W is an increasing function of
Cn. Plausible mechanisms are proposed to explain the experimental results, by comparing them with those obtained for other bacterial species such as
Proteus mirabilis and
Bacillus subtilis.
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Mutsumi Mitobe, Kousuke Yakubo
2009 Volume 78 Issue 7 Pages
074006
Published: July 15, 2009
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General form of the probability distribution function (PDF) of the rescaled fractal dimension characterizing spatial structures of local order parameters in finite but large systems near the critical point is derived. To obtain the PDF, we assume that (i) sample-to-sample fluctuations of global order parameters are described by the generalized Gumbel distribution function, which is known to be valid for many of long-range correlated systems such as critical systems and (ii) spatial structures of local order parameters are always fractal at the critical point. From the obtained PDF, it is elucidated that fluctuations of fractal dimensions do not exhibit a universal character in contrast to the case of fluctuating global order parameters. In addition, we perform numerical calculations of the PDF for two-dimensional percolation systems near the critical concentration and confirm that the analytically calculated PDF well describes numerical results. We also discuss the influence of non-fractal critical clusters neglected under the assumption (ii).
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Hiroyuki Suzuki, Youhei Fujitani
2009 Volume 78 Issue 7 Pages
074007
Published: July 15, 2009
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In carrying a Brownian particle by means of an external force in one dimension from a place to another in a finite time lapse, we consider controlling the force using a feedback loop to minimize an evaluation functional. The evaluation functional contains the average of the work done to the particle by the force and two terms involving control parameters. One is a term proportional to the mean squared force, while the other is a term proportional to the mean squared distance between the final particle position and the destination. Solving differential equations numerically, we calculate the average work under optimal control for various values of control parameters and find the calculated values bounded from below. The average work is also shown to be larger as we utilize less information on the state of the particle in the feedback control by decreasing the number of observed variables and by increasing the noise amplitude in the observation.
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Hiroyasu Ejiri
2009 Volume 78 Issue 7 Pages
074201
Published: July 15, 2009
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Experimental nuclear matrix elements
M2ν for two neutrino double beta decays (2νββ) are discussed in terms of experimental nuclear matrix elements for successive single-β processes via Fermi-surface (low-lying) quasi-particle states (FSQP). They are reproduced approximately by the sum Σ
LMk of the 2νββ matrix elements
Mk through
k-th intermediate quasi-particle states in the Fermi-surface.
Mk is expressed by using the
GT(
Jπ=1
+) matrix elements of
Mi(
k) and
Mf(
k) for the successive single-β transitions through the
k-th intermediate state. The single-β matrix elements are evaluated from experimental data of single-β, EC and charge exchange reactions.
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Hidenori Hasimoto
2009 Volume 78 Issue 7 Pages
074401
Published: July 15, 2009
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A doubly periodic fundamental solution of the Stokes equations is constructed on the basis of the author’s fundamental solution of a Poisson equation recently published in this Journal. It is represented by the Weierstrass elliptic function in the complex plane. As an example of its application, a generalized Darcy law for a lattice of thin circular cylinders is derived using the general solution extended from the fundamental solution.
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Hirotaka Shimizu, Sakae Araki, Yoshisato Funahashi, Yosuke Honda, Tosh ...
2009 Volume 78 Issue 7 Pages
074501
Published: July 15, 2009
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We studied γ-ray generation by the laser-Compton scattering using a Fabry–Perot optical resonant cavity at the KEK-ATF electron storage ring. The laser power was enhanced up to 388 W in the optical resonant cavity with an injection power of 7 W in the ATF operation environments. The yield of photons for a crossing of a laser pulse and an electron bunch was 3.3±0.6, which was consistent with a numerical estimate. In this paper, we report construction, installation and future prospect toward the polarized positron generation for the International Linear Collider.
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Akihiro Koga, Satoshi Ohmura, Fuyuki Shimojo
2009 Volume 78 Issue 7 Pages
074601
Published: July 15, 2009
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The structural properties of a molecular liquid consisting of Cl–Se–Se–Cl molecules are studied by
ab initio molecular-dynamics simulations. The calculated structure factor is shown to be in good agreement with the experimental results. It is seen that while neighboring molecules have only a small effect on intramolecular parameters such as bond lengths and bond angles, the intermolecular orientational correlations depend largely on the distance between molecules. The interaction energy between two molecules is investigated to explore the molecular arrangement in the liquid state. A weak attractive interaction is found to exist among molecules, which plays an important role for short-range intermolecular correlations.
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Yutaka Moritomo, Kazuhiro Igarashi, Tomoyuki Matsuda, Jungeun Kim
2009 Volume 78 Issue 7 Pages
074602
Published: July 15, 2009
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Lattice structure of hole-doped Na
1.6−xCo[Fe(CN)
6]
0.902.9H
2O was systematically investigated against doping level (
x) and temperature (
T) by means of synchrotron-radiation powder diffraction. We found that the hole-doping procedure on the Co site induces a rhombohedral–cubic structural phase transition. The rhombohedral phase (cubic phase) is observed in
x≤0.02 and 100≤
T≤300 K (
x≥0.14 and 100≤
T≤300 K), while two lattice structures coexist in the intermediate-
x region (0.02≤
x≤0.14). We interpreted the two-phase region of the
x–
T phase diagram in terms of
intrinsic phase separation into large-
x (Na
+-poor) and small-
x (Na
+-rich) regions, because the Na
+ ions can migrate within the crystal to minimize the total free energy.
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Yu Yoshioka, Kazumasa Miyake
2009 Volume 78 Issue 7 Pages
074701
Published: July 15, 2009
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The anisotropy of the
d-vector of the spin-triplet superconductor Sr
2RuO
4 is investigated on the basis of a
d–
p model where the Coulomb interaction
Upp at the O site is taken into account together with
Udd at the Ru site. It is shown in the third-order perturbation for the pairing interaction that
Upp induces the spin-triplet pairing of (sin
px+
isin
py) symmetry. The piaring state with the
d-vector in the RuO
2 plane is stabilized by the atomic spin–orbit interaction and Hund’s rule coupling at the Ru site, in contrast to the result based on the multiband Hubbard model without
Upp. This result is consistent with that obtained by the Knight shift measurement.
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Shuta Tahara, Satoru Ohno, Tatsuya Okada
2009 Volume 78 Issue 7 Pages
074702
Published: July 15, 2009
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The measurements of the magnetic susceptibility χ of liquid transition metal–Al alloys were carried out during cooling from about 1600 °C to the melting point. The χ’s of liquid Ni
1−cAl
c with
c≥0.3, Co
1−cAl
c with
c≥0.6, and Fe
1−cAl
c with
c≥0.8 have positive and weak temperature dependences, which suggests that the Ni, Co, and Fe ions in their liquid alloys are in the nonmagnetic state. Liquid Mn
0.1Al
0.9, Cr
1−cAl
c with
c≥0.5, V
1−cAl
c with
c≥0.8, and Ti
1−cAl
c with
c≥0.5 were also found to be in the nonmagnetic state. The magnetic susceptibility of their liquid alloys in the nonmagnetic state has been studied using the Anderson model. On the other hand, liquid Ni
1−cAl
c with
c≤0.2, Co
1−cAl
c with
c≤0.5, Fe
1−cAl
c with
c≤0.7, and Mn
1−cAl
c with 0.3≤
c≤0.7 show the Curie–Weiss behavior. Reasonable parameters of the Curie–Weiss law for their liquid alloys can be obtained by plotting 1⁄χ vs
T and χ vs 1⁄
T.
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Masato Matsuura, Yoshiyuki Yoshida, Hiroshi Eisaki, Nobuhisa Kaneko, C ...
2009 Volume 78 Issue 7 Pages
074703
Published: July 15, 2009
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We measured the inelastic neutron scattering of slightly overdoped high-
Tc superconductor Bi
2.1Sr
1.9CaCu
2O
8+δ (Bi2212:
Tc=86.2±3.5 K). We observed the enhancement of a commensurate peak at (1⁄2,1⁄2,−14) and ω∼34 meV in the superconducting state, which is similar to the previously reported resonance peak in the YBa
2Cu
3O
6+x (YBCO) and Bi2212 systems. However, the temperature dependence above
Tc is different: substantial resonance spectral weight remains above
Tc, and shows a sharp drop at
T∼200 K, which roughly agrees with the onset of the pseudogap (
T*). We propose that the different thermal variations of the magnetic excitations in high-
Tc superconductors can be understood in terms of the pseudogap phase and redistribution of the magnetic spectral weight across
Tc and
T*.
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Shigemasa Suga, Akira Sekiyama, Shin Imada, Junichi Yamaguchi, Akihiko ...
2009 Volume 78 Issue 7 Pages
074704
Published: July 15, 2009
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By combining the high resolution hard and soft X-ray photoelectron spectroscopy, the Yb 3d and 4f states in the strongly correlated electron system, YbInCu
4, are studied. After high accuracy experimental determination of the four unknown physical quantities such as the valence values and thicknesses of the surface and sub-surface regions, genuine behaviors of the Kondo resonance as well as the electronic structures in the bulk and sub-surface are clarified. A clear first order valence transition in the bulk and a gradual valence change in the sub-surface region with temperature are revealed.
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Takao Suzuki, Fumiko Yamada, Isao Watanabe, Teiichiro Matsuzaki, Takay ...
2009 Volume 78 Issue 7 Pages
074705
Published: July 15, 2009
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Zero- and longitudinal-field muon-spin-relaxation (ZF- and LF-μSR) measurements were carried out down to
T=20 mK on the slightly doped quantum spin system TlCu
1−xMg
xCl
3 with
x=0.0047, in which a magnetic phase transition is observed at 0.70 K by specific heat measurement. LF-μSR measurements above and below the phase transition temperature revealed that the impurity-induced magnetic moments of the Cu-3
d spins slowly fluctuate at a frequency of 0.74 MHz at
T=20 mK, far below the magnetic phase transition temperature. It is possible that the impurity-induced magnetic moments are in an exotic state where they fluctuate while preserving their wave vector and relative phase, i.e.,
a coherently fluctuating state.
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Christoph Meingast, Akira Inaba, Rolf Heid, Volker Pankoke, Klaus-Pete ...
2009 Volume 78 Issue 7 Pages
074706
Published: July 15, 2009
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The specific heat of YBa
2Cu
3O
x (
x=6.7, 6.9, and 7.0) has been determined to within 0.1% accuracy from 5 to 400 K using adiabatic calorimetry. The phonon specific heat contribution for
x=7.0 is calculated using
ab-initio LDA and subtracted from the experimental data, yielding estimates of the oxygen-ordering and electronic heat capacity contributions. The oxygen-ordering contribution agrees well with theoretical predictions. Although the LDA phonon heat capacity is found to be very accurate, it is not quite precise enough to reliably determine the electronic term over the whole temperature range. We demonstrate how small changes in the phonon density of states can affect the results, which underlines the extreme difficulty in accurately determining the electronic heat capacity of YBa
2Cu
3O
x.
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Wataru Izumida, Kentaro Sato, Riichiro Saito
2009 Volume 78 Issue 7 Pages
074707
Published: July 15, 2009
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Energy band for single wall carbon nanotubes with spin–orbit interaction is calculated using non-orthogonal tight-binding method. A Bloch function with spin degree of freedom is introduced to adapt the screw symmetry of nanotubes. The energy gap opened by spin–orbit interaction for armchair nanotubes, and the energy band splitting for chiral and zigzag nanotubes are evaluated quantitatively. Spin polarization direction for each split band is shown to be parallel to the nanotube axis. The energy gap and the energy splitting depend on the diameter and chirality in an energy scale of sub-milli-electron volt. An effective model for reproducing the low energy band structure shows that the two mechanism of the band modification, shift of the energy band in two dimensional reciprocal lattice space, and, effective Zeeman energy shift, are relevant. The effective model explains well the energy gap and splitting for more than 300 nanotubes within the diameter between 0.7 to 2.5 nm.
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Shintaro Nakamura, Tsutomu Nojima, Akira Yoshihara, Shigehiro Ohnuma, ...
2009 Volume 78 Issue 7 Pages
074708
Published: July 15, 2009
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We investigate the electrical resistivity of the ferromagnetic granular thin films TM–Al–O (TM=Fe, Co). The resistivity shows
T2 behavior at low temperatures in all metallic samples. This strongly suggests scattering of conduction electrons by thermally excited ferromagnetic spin waves. Logarithmic Kondo like behavior (−log
T) in the resistivity and negative magnetoresistivity at low temperatures are observed. With decreasing concentration of transition metal, both the coefficients of the
T2 and log
T terms increase.
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Shinya Nishiyama, Kazumasa Miyake
2009 Volume 78 Issue 7 Pages
074709
Published: July 15, 2009
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On the basis of de Gennes’ formalism, it is shown that the effect of the long-time-tail in the “force correlation function”, due to the diffusion process of the magnetization of conduction electrons (for the correlation function of the time-reversal operator
K), gives rise to an excess suppression of the superconducting transition temperature
Tc of conventional superconductors with magnetic impurities. The suppression of
Tc is prominent in the one-dimensional case, while those in two- and three-dimensional cases are almost invisible for realistic values of parameter for the quantum correction.
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Koji Kaneko, Naoto Metoki, Hiroyuki Kimura, Yukio Noda, Tatsuma D. Mat ...
2009 Volume 78 Issue 7 Pages
074710
Published: July 15, 2009
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In order to obtain a detailed picture of rattling in PrOs
4Sb
12, a single crystal neutron diffraction experiment and a maximum-entropy analysis were carried out. At room temperature, a widely distributed anisotropic Pr nuclear density in the Sb icosahedron cage was revealed. An unusual trapezoidal form in the cross-sectional density profile of Pr clearly demonstrates the presence of strong anharmonicity in the Pr potential, in which the ‹111› direction has the maximum spread. The highest density is found at an off-center position along the same direction. The Pr density distribution becomes isotropic and sharp by cooling down to 8 K. Moreover, the highest density of Pr at 8 K is found at the center of the cage. The obtained nuclear density distribution and its temperature variation indicate that the rattling in PrOs
4Sb
12 is a strong anharmonic thermal motion without an off-center potential minimum.
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Takuma Kawai, Atsushi Kawamoto
2009 Volume 78 Issue 7 Pages
074711
Published: July 15, 2009
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The pattern of charge ordering of the quasi two-dimensional organic conductor, α-(BEDT-TTF)
2I
3 [BEDT-TTF: bis(ethylenedithio)tetrathiafulevalene], provides important information about the usual transport properties of this salt. Experiments on this salt have yielded conflicting results. Especially, the results of nuclear magnetic resonance (NMR) measurement and X-ray Diffraction (XRD) study have suggested contradictory charge patterns. To clarify these discrepancies, we performed
13C-NMR measurements using a single side
13C enriched molecule. Above the metal–insulator transition temperature, the spin susceptibility at the B site decreased and that at the C site increased with decreasing temperature. Below the metal–insulator (M–I) transition temperature, however, the angular dependence of the NMR shift suggested that the charge order pattern was a horizontal stripe, in which the A(A′) and B molecules are charge rich sites and the A′(A) and C molecules are charge poor.
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Yoshikazu Mizuguchi, Fumiaki Tomioka, Shunsuke Tsuda, Takahide Yamaguc ...
2009 Volume 78 Issue 7 Pages
074712
Published: July 15, 2009
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We have investigated the effect of atomic substitutions in the FeSe system, which exhibits the simplest crystal structure among the iron-based superconductors. An enhancement of the superconducting transition temperature
Tc was observed with the substitution of S or Te for Se; the
Tc increased with S substitution by up to 20%, and also increased with Te substitution up to 75%. In contrast, Co or Ni substitutions for the Fe site significantly suppressed superconductivity. In this work we present a detailed description of the substitution technique employed to determine
Tc in the FeSe system.
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Fawei Zheng, Ken-ichi Sasaki, Riichiro Saito, Wenhui Duan, Bing-Lin Gu
2009 Volume 78 Issue 7 Pages
074713
Published: July 15, 2009
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Tight-binding (TB) calculation for zigzag boron nitride nanoribbons (ZBNNRs) is presented. The TB parameters are obtained so as to reproduce density functional calculation. The analytical expressions of boron (nitrogen) edge states that lie near the bottom (top) of conductance (valence) bands are given. The modification of the potential near the edge is found to be important in explaining the small energy dispersion of the edge states. The energy band gap of ZBNNR decreases with increasing ribbon width, which is explained by the edge potential. We also discuss the half metallicity for ZBNNR by considering the Hubbard-type Coulomb interaction.
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Georg Knebel, Dai Aoki, Gerard Lapertot, Bernard Salce, Jacques Flouqu ...
2009 Volume 78 Issue 7 Pages
074714
Published: July 15, 2009
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We present a detailed study of the high pressure phase diagram of the non-centrosymmetric antiferromagnet CeCoGe
3 by measurements of the ac calorimetry in a diamond anvil pressure cell. Under high pressure the magnetic ordering temperature shows a step like decrease due to various successive magnetic phases under high pressure. The magnetic order disappears at a critical pressure of
pc≈5.5 GPa. Around the critical pressure bulk superconductivity has been detected in the ac calorimetric measurement.
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Shugo Suzuki, Toshihiro Ariizumi, Ming-Fang Li
2009 Volume 78 Issue 7 Pages
074715
Published: July 15, 2009
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We study the X-ray magnetic circular dichroism (XMCD) spectra at the U
M4,5 and
N4,5 edges of uranium monochalcogenides, U
X where
X=S, Se, and Te, examining the applicability of the XMCD sum rules to U
X by the fully relativistic full-potential linear-combination-of-atomic-orbitals (LCAO) method based on the density functional theory. To extract the transitions relevant to the sum-rule analysis, we employ the Mulliken population analysis (MPA). Using the MPA, the orbital sum rule is found to be valid to 10–20% for the
M4,5 edges and valid to 5–15% for the
N4,5 edges. On the other hand, the spin sum rule is found to be valid to 10–20% for the
M4,5 edges whereas valid to 30–35% for the
N4,5 edges. Furthermore, it is found that the calculated XMCD spectra are consistent with a recent experimental observation that the intensity of the
N4,5 XMCD signal is comparable to that of the
M4,5 XMCD signal although contradicting a previous theoretical prediction that the XMCD intensity at the
N4,5 edges is one order of magnitude smaller than that at the
M4,5 edges.
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Yasuo Yoshida, Tatsuya Kawae, Yuko Hosokoshi, Katsuya Inoue, Nobuya Ma ...
2009 Volume 78 Issue 7 Pages
074716
Published: July 15, 2009
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We have measured the specific heat of the
S=1⁄2 alternating-bond Heisenberg antiferromagnetic chain compound pentafluorophenyl nitronyl nitroxide in magnetic fields using a single crystal and powder. A sharp peak due to field-induced magnetic ordering (FIMO) is observed in both samples. The
H–
T phase boundary of the FIMO of the single crystal is symmetric with respect to the central field of the gapless field region
HC1≤
H≤
HC2, whereas it is distorted for the powder whose ordering temperatures are lower. We discuss possibility that an effective pressure caused by mixing the powder with grease, which is reported for various organic compounds, plays an important role for the distorted phase boundary. An analysis employing calculations based on the finite temperature density matrix renormalization group suggests that the pressure-induced frustration enhances incommensurate spin correlation leading to the distorted phase boundary for the powder.
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Yasumasa Hasegawa, Hirotoshi Taniguchi
2009 Volume 78 Issue 7 Pages
074717
Published: July 15, 2009
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We show that the two superconducting transition temperatures observed in CePt
3Si [higher transition temperature (0.75 K) in as-cast samples and lower transition temperature (0.45 K) in annealed samples and single crystals] are due to the pair breaking effect of spin–orbit coupling. By assuming that the local electric field due to the lack of inversion symmetry is large in the annealed samples and very small in the as-cast samples, the difference in transition temperature is explained by the order parameter of the triplet superconductivity as
d(
k)∝(
kz,0,0) or (0,
kz,0). This
d vector is caused by interplane coupling and is consistent with the constant Knight shift in the superconducting state in any direction of the magnetic field. The possibility of obtaining Cooper pairs with a finite total momentum (Fulde–Ferrell–Larkin–Ovchinnikov state) caused by spin–orbit coupling is studied.
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Kazumasa Horigane, Haruhiro Hiraka, Kenji Ohoyama
2009 Volume 78 Issue 7 Pages
074718
Published: July 15, 2009
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We determined the crystal structural parameters of FeSe
1−xTe
x (
x=0.5, 0.625, 0.75, 0.875) and FeSe by using the neutron powder diffraction technique. It was found that the superconducting transition temperature
Tc of FeSe
1−xTe
x increased with the (Se,Te)–Fe–(Se,Te) bond angle α in the Te-doped samples. However,
Tc of FeSe did not exhibit a similar relation. In order to explain this contradiction, we studied the temperature dependence of the
z position of chalcogens, which is strongly coupled to the spin fluctuation by theoretical calculations. The
z position in FeSe showed a remarkable shift, indicating that strong spin fluctuation can affect the superconductivity in FeSe.
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Shintaro Hoshino, Junya Otsuki, Yoshio Kuramoto
2009 Volume 78 Issue 7 Pages
074719
Published: July 15, 2009
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Dynamical properties are studied numerically for a variant of the Kondo model with singlet and triplet crystalline electric field (CEF) levels where Kondo and CEF singlets compete for the ground state. Using the continuous-time quantum Monte Carlo method, we derive the
t-matrix of conduction electrons and dynamical susceptibilities of local electrons without encountering the negative sign problem. When the CEF splitting is comparable to the Kondo temperature, the dynamical response has only a quasi-elastic peak. Nevertheless, the local single-particle spectrum shows an energy gap in strong contrast with the ordinary Kondo model.
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Hiroshi Matsui, Jing Ju, Tomohiro Odaira, Naoki Toyota
2009 Volume 78 Issue 7 Pages
074801
Published: July 15, 2009
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Two-dimensionally confined water in between the MnO
2 octahedral layers in Na-birnessite has been studied to clarify the physical properties and the structural arrangements. From the analysis employing an inductively coupled plasma (ICP) method and chemical titration, the chemical composition is determined to be Na
0.28Mn
4+0.73Mn
3+0.27O
2 yH
2O in our sample. According to the X-ray diffraction (XRD) experiments, the interlayer distance along the
c axis is 7.17 Å at 293 K in atmosphere, though the distance shrinks to 5.77 Å when the sample is kept either at 333 K in atmosphere or at 293 K in vacuum. The weight loss obtained by thermogravimetry exhibits two steps caused by the dehydration in atmosphere. Together with the XRD data, we confirm that there are two contributions of the water in the interlayers; weakly hydrated water and strongly hydrated water. The latter is regarded as a structural water to maintain the layer structure. In the infrared spectra, three novel peaks are found to develop in evacuating the sample. These peaks are associated with three different distances in between oxygen atoms of water molecules identified by the precise X-ray studies so far. We consider that Na
+ ion locates approximately at one MnO
2 unit with Mn
3+ among the four MnO
2 units to preserve charge valence, and the strongly hydrated water molecules surround Na
+ in the form of a quasi-planer hexamer-like cluster reflecting the symmetry of MnO
2 layer. The strict restriction of water to the plane and the Coulomb repulsion between Na
+ may induce a deformation of the cluster leading to the abovementioned three different distances.
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Kohei Motegi
2009 Volume 78 Issue 7 Pages
075001
Published: July 15, 2009
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Takeshi Koyama, Makoto Nakajima, Tohru Suemoto
2009 Volume 78 Issue 7 Pages
075002
Published: July 15, 2009
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Minki Jeong, Myeonghun Song, Tomohiro Ueno, Takao Mizusaki, Akira Mats ...
2009 Volume 78 Issue 7 Pages
075003
Published: July 15, 2009
Released on J-STAGE: December 28, 2011
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