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Kazushi Mimura
2009 Volume 78 Issue 3 Pages
033001
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We have applied the generating functional analysis (GFA) to the continuous Hopfield model. We have also confirmed that the GFA predictions in some typical cases exhibit good consistency with computer simulation results. When a retarded self-interaction term is omitted, the GFA result becomes identical to that obtained using the statistical neurodynamics as well as the case of the sequential binary Hopfield model.
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Yasuki Nagai, Yuichi Hatsukawa
2009 Volume 78 Issue 3 Pages
033201
Published: March 15, 2009
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We have proposed a new route to produce
99Mo for nuclear medicine by the
100Mo(
n,2
n)
99Mo reaction. The reaction cross section is known to be ∼1.5 b in the neutron energy,
En, range from 12 to 17 MeV: 10-times larger than the thermal-neutron capture cross section of
98Mo. By irradiating an enriched
100Mo target for 198 h with neutrons of ∼10
13 n/(cm
2 s) at
En∼14 MeV, one can produce 79 GBq/g specific activity of
99Mo. Since the cross sections for
100Mo(
n,
p)
100Nb,
100Mo(
n,
np)
99Nb and
100Mo(
n,α)
97Zr at 12≤
En≤17 MeV are small, less than a few mb, radioactive waste during and/or after chemical processing of
99Mo would not be a serious problem. The proposed route could bring a major breakthrough in the solution of ensuring a constant and reliable supply of
99Mo without using highly enriched
235U.
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Hiroshi Akiba, Shinto Nakano, Yutaka Nishio, Koji Kajita, Biao Zhou, A ...
2009 Volume 78 Issue 3 Pages
033601
Published: March 15, 2009
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In this study, we have investigated a quasi-two-dimensional organic conductor, λ-BETS
2FeCl
4, that exhibits a phase transition from a paramagnetic metal to an antiferromagnetic (AF) insulator at a critical temperature (
TMI∼8.3 K). To investigate the mechanism of a notable phase transition, we studied the thermal properties of the conductor for temperatures down to 0.2 K at zero magnetic field. We observed that the specific heat of the conductor showed a sharp peak at
TMI and a Schottky-type hump. The temperature dependence of the excess specific heat clarifies that π and 3d spins do not cooperatively form an AF order at
TMI. We concluded that a 3d spin system keeps a paramagnetic state even at the lowest studied temperature.
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Kohsuke Inomata, Shigenori Tsuji, Yohsuke Yoshinari, Hyun Soon Park, D ...
2009 Volume 78 Issue 3 Pages
033602
Published: March 15, 2009
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We report a cantilever resonance frequency shift due to the magnetic resonance force gradient in magnetic resonance force microscopy. Our experimental results obtained for a phantom sample of diphenylpicrylhydrazil (DPPH) at
T=14 K can be quantitatively understood with the magnetic force gradient containing the first derivative of spin magnetization. This substantial contribution should be explicitly treated when calculating an equipment function and estimating the number of spins through the deconvolution process for image restoration.
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Shinji Watanabe, Masatoshi Imada
2009 Volume 78 Issue 3 Pages
033603
Published: March 15, 2009
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We theoretically study the stability of the solidified second-layer
3He at 4/7 of the first-layer density adsorbed on graphite, which exhibits quantum spin liquid. We construct a lattice model for the second-layer
3He by taking account of density fluctuations on the third layer together by employing the refined configuration recently found by path integral Monte Carlo simulations. When holes are doped into the 4/7 solid, within the mean-field approximation, the density-ordered fluid emerges. The evolution of hole pockets offers a unified explanation for the measured doping and temperature dependences of specific-heat anomalies. We argue that differentiation in momentum space is a key to understanding the physics and accounts for multiscale thermodynamic anomalies in the mono- and double-layered
3He systems beyond the mean-field level.
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Mitsunori Hieda, Kenji Matsuda, Tsuyoshi Kato, Taku Matsushita, Nobuo ...
2009 Volume 78 Issue 3 Pages
033604
Published: March 15, 2009
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We observed the frequency dependence of the superfluid transition of
4He films adsorbed on planar gold up to a very high frequency of 180 MHz, using the overtone harmonic modes of a quartz crystal microbalance. The superfluid onset was observed at a temperature markedly higher than the Kosterlitz–Thouless (KT) transition temperature, the onset temperature in the low-frequency limit. The observed frequency dependence is surprisingly well reproduced by the dynamic theory close to the high-frequency condition where the vortex diffusion length in a period becomes as small as the vortex core diameter. We also observed that the superfluid vortex parameters depend strongly on the kind of substrate as well as on
4He film thickness.
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Yoshihiko Okamoto, Hiroyuki Yoshida, Zenji Hiroi
2009 Volume 78 Issue 3 Pages
033701
Published: March 15, 2009
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A polycrystalline sample of vesignieite BaCu
3V
2O
8(OH)
2 comprising a nearly ideal kagome lattice composed of Cu
2+ ions carrying spin 1/2 has been synthesized and studied by magnetization and heat capacity measurements. Magnetic susceptibility shows a neither long range order, a spin glass transition nor a spin gap down to 2 K, in spite of a moderately strong antiferromagnetic interaction of
J⁄
kB=53 K between nearest-neighbor spins. A broad peak observed at a temperature corresponding to 0.4
J in intrinsic magnetic susceptibility indicates a marked development of the short-range order. The ground state of vesignieite is probably a gapless spin liquid or is accompanied by a very small gap less than ∼
J⁄30.
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Masatomo Uehara, Akira Uehara, Katsuya Kozawa, Yoshihide Kimishima
2009 Volume 78 Issue 3 Pages
033702
Published: March 15, 2009
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We have synthesized a new superconductor ZnN
yNi
3 with
Tc∼3 K. The crystal structure is of the same antiperovskite-type as MgCNi
3 and CdCNi
3. As far as we know, this is the third superconducting material in the Ni-based antiperovskite series and the first antiperovskite nitride superconducting material. For this new superconductor, the lower critical field
Hc1(0), upper critical field
Hc2(0), coherence length ξ(0), penetration depth λ(0), Ginzburg–Landau parameter κ(0), electronic specific heat coefficient γ, and Debye temperature Θ
D have been experimentally determined.
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Daisuke Matsubayashi, Masafumi Udagawa, Masao Ogata
2009 Volume 78 Issue 3 Pages
033703
Published: March 15, 2009
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We study current-induced dynamics of a magnetic domain wall by solving a time-dependent Schrödinger equation combined with Landau–Lifshitz–Gilbert equation in a one-dimensional electron system coupled to localized spins. Two types of domain-wall motions are observed depending on the hard-axis anisotropy,
K⊥, of the localized spin system. For small values of
K⊥, the magnetic domain wall shows a streaming motion driven by spin transfer. In contrast, for large values of
K⊥, a stick-slip motion driven by momentum transfer is obtained. We clarify the origin of these characters of domain-wall motions in terms of the dynamics of one-particle energy levels and distribution functions.
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Hideto Fukazawa, Takehiro Yamazaki, Kenji Kondo, Yoh Kohori, Nao Takes ...
2009 Volume 78 Issue 3 Pages
033704
Published: March 15, 2009
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We report the
75As nuclear magnetic resonance (NMR) measurement of the hole-doped superconductor Ba
1−xK
xFe
2As
2 with different lattice parameters and different superconducting volume fractions (
Tc\\simeq38 K).
75As-NMR spectra revealed that the magnetically ordered and superconducting phases are microscopically separated. The spin-lattice relaxation rate 1⁄
T1 in the normal state reflects the existence of a large two-dimensional antiferromagnetic spin fluctuation. The 1⁄
T1 in the superconducting state down to the lowest measurement temperature
T varies close to
T3. In addition, it exhibits no coherence peak just below
Tc. This shows a
T dependence similar to those of other iron pnictides.
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Takaaki Morie, Toshiro Sakakibara, Hiroyuki S. Suzuki, Hiroshi Tanida, ...
2009 Volume 78 Issue 3 Pages
033705
Published: March 15, 2009
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Magnetizations of single crystals of cubic PrMg
3 with a Γ
3 non-Kramers doublet ground state have been examined at very low temperatures down to 60 mK in magnetic fields up to 8.5 T. No evidence of a long-range order is obtained. Instead, the magnetic susceptibility for both [001] and [111] directions continuously increases on cooling below 3 K where the system is well in the Van-Vleck paramagnetic regime, followed by a steep rise due to Pr nuclear Curie law below ∼0.2 K. Subtracting the nuclear contribution from the total magnetization yields a −log
T (1≤
T≤10 K) or a −\\sqrt
T (0.3≤
T≤2.5 K) dependence of the 4
f-electronic susceptibility. We argue that a possible random site exchange effect in this Heusler type compound is not the origin of the unusual increase of the susceptibility. Our observations strongly suggest the presence of a hybridization effect between Pr 4
f and conduction electrons.
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Taichi Terashima, Motoi Kimata, Hidetaka Satsukawa, Atsushi Harada, Ka ...
2009 Volume 78 Issue 3 Pages
033706
Published: March 15, 2009
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We report measurements of the de Haas–van Alphen (dHvA) oscillation and a band structure calculation for the pnictide superconductor BaNi
2P
2, which is isostructural to BaFe
2As
2, the mother compound of the iron-pnictide high-
Tc superconductor (Ba
1−xK
x)Fe
2As
2. Six dHvA-frequency branches with frequencies up to ∼8 kT were observed, and they are in excellent agreement with results of the band-structure calculation. The determined Fermi surface is large, enclosing about one electron and hole per formula unit, and three-dimensional. This is in contrast to the small two-dimensional Fermi surface expected for the iron-pnictide high-
Tc superconductors. The mass enhancement is about two.
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Toshiya Inami, Kenji Ohwada, Yasuhiro H. Matsuda, Zhong Wen Ouyang, Hi ...
2009 Volume 78 Issue 3 Pages
033707
Published: March 15, 2009
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Resonant magnetic x-ray diffraction experiments on the Shastry–Sutherland lattice TbB
4 were carried out under pulsed magnetic fields up to 30 T at 8 K. TbB
4 exhibits a multi-step magnetization process above 16 T below about 20 K when magnetic fields are applied along the
c-axis. We examined the intensity of the 010 magnetic reflection as a function of magnetic field and found that the magnetization plateau phases are accompanied by large XY components of magnetic moments. We propose novel magnetic structures which consist of XY spins and Ising spins for the plateau phases. We also propose that energy level crossing and its inherent degeneracy give rise to the successive metamagnetic transitions in TbB
4.
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Masahiro Hotta
2009 Volume 78 Issue 3 Pages
034001
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We propose a protocol of quantum energy teleportation that transports energy in spin chains to distant sites by only local operations and classical communication. The protocol uses ground-state entanglement and localized negative-energy excitation, and the energy is teleported without breaking any physical laws including causality and local energy conservation.
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Hiroshi Tanaka, Asumi Nakajima, Akinobu Nishiyama, Tetsuji Tokihiro
2009 Volume 78 Issue 3 Pages
034002
Published: March 15, 2009
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A differential equation exhibiting replicative time-evolution patterns is derived by inverse ultradiscretizatrion of Fredkin’s game, which is one of the simplest replicative cellular automaton (CA) in two dimensions. This is achieved by employing a certain filter and a clock function in the equation. These techniques are applicable to the inverse ultra-discretization (IUD) of other CA and stabilize the time-evolution of the obtained differential equation. Application to the game of life, another CA in two dimensions, is also presented.
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Takeshi Sugimori, Hiroyuki Hyuga, Yukio Saito
2009 Volume 78 Issue 3 Pages
034003
Published: March 15, 2009
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We study a possibility for chiral symmetry breaking to take place without autocatalytic process in an open system. Our model consists of an inflow of enantiomers and outflow of heterogeneous dimers from the system, which corresponds to the Frank model without autocatalysis. It is demonstrated analytically as well as numerically that the rate equations for this system does not predict any kind of symmetry breaking but the stochastic master equation predicts that the system approaches asymptotically a homochiral state. This is caused by the fluctuations induced by the discreteness of population numbers of enantiomers in their perpetual flow. It is argued that this scenario can be effective for a very small open system and could be a candidate for an initial chiral imbalance.
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Akira Taniguchi, Yuhei Natsume
2009 Volume 78 Issue 3 Pages
034004
Published: March 15, 2009
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We performed simulations of interference where two anisotropic condensates have multiple vortices. The problem of how the multiple zipper pattern (MZP) appears is investigated on the basis of the time-dependent Gross–Pitaevskii equation. The anisotropic multiple-vortex state, which is a linear combination of eigen states of anisotropic harmonic potential Hamiltonian is used to reproduce the observed MZP. Multiple vortices are expressed by high winding numbers in a calculation. In the isotropic case, the MZP can be found only in the central region with a low density due to the large vortex core. In the anisotropic and high winding number case, the MZP with several dislocations appears. In fact, the MZP is clearly seen because of high density. Each wave function of the anisotropic multiple-vortex state is divided into two parts. In short, four wave packets form the MZP. Both the large anisotropy and high winding number are required in reproducing the MZP.
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Masayuki Kawamura, Wei-Guo Jin, Nobuyuki Takahashi, Tatsuya Minowa
2009 Volume 78 Issue 3 Pages
034301
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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High-resolution atomic-beam laser spectroscopy has been performed to study the Stark effect of K atoms. A compact electrode apparatus has been developed to produce a stable and strong electric field. The Stark shifts of the
D1 and
D2 lines as well as the splitting of the
D2 line have been measured and found to be proportional to the square of the electric field. The scalar polarizability of the
D1 line and the scalar and tensor polarizabilities of the
D2 line have been determined to be α
s (4
p2P1⁄2)−α
s (4
s2S1⁄2)=81.3±2.4 kHz/(kV/cm)
2, α
s (4
p2P3⁄2)−α
s (4
s2S1⁄2)=93.0±2.5 kHz/(kV/cm)
2, and α
t (4
p2P3⁄2)=−27.6±0.7 kHz/(kV/cm)
2, respectively, providing a crosscheck of the previously reported values.
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Yusuke Doi, Kazuyuki Yoshimura
2009 Volume 78 Issue 3 Pages
034401
Published: March 15, 2009
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Moving discrete breather (DB) is investigated in a four particle lattice. We introduce a parametrized lattice model, which is an extension of the Fermi–Pasta–Ulam (FPU) β lattice. This lattice model possesses an additional first integral for a particular parameter value, which we call the symmetric lattice case. We propose a new numerical method for precisely calculating moving DB solutions in the FPU-β lattice: the method continues the moving DB solution from the symmetric lattice case. It is shown that DB’s velocity can take any value, even over the sound velocity of the linear lattice.
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Yuko Aoyanagi, Ko Okumura
2009 Volume 78 Issue 3 Pages
034402
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We revisit the standard elastic-plastic fracture theory developed by Hutchinson, Rice, and Rosengren (HRR) and reproduce, by a simple scaling argument, the stress singularity around the crack tip derived by HRR. From the singular behavior thus reconfirmed, we propose a general scaling relation which guarantees an effect similar to the tip-blunting effect: the maximum stress at the crack tip in a structured material can be reduced by increasing the structure size. This proposed relation is explicitly confirmed by numerical calculations performed for a coarse-grained lattice model, and leads to general scaling relations for fracture surface energy and to a possible reinforcement of cellular solids due to the pores.
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Koichi Matsumoto, Hiroyuki Tsuboya, Keiichi Yoshino, Satoshi Abe, Hiro ...
2009 Volume 78 Issue 3 Pages
034601
Published: March 15, 2009
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The freezing and melting of
4He in various aerogels with porosities ranging from 92 to 97% were studied using longitudinal ultrasound. The freezing pressure, detected from changes in velocity and attenuation, was elevated compared with that of the bulk by about 0.3 MPa, and showed a weak dependence on aerogel porosity. Inside the aerogels, there was a liquid phase, a solid phase or a coexisting state depending on temperature and pressure of the sample. We report the measurement of the transmission of sound through the solid–liquid interface in aerogel for the first time, which was independent of temperature and unaffected by a small addition of
3He, unlike that at the bulk interface. This indicates that sound attenuation at the interface is due to the disorder, originating from silica strands. Small amounts of
3He in the solid significantly decreased attenuation, because the resultant pinning of dislocations by
3He suppressed phonon scattering, as is observed in bulk solid
4He.
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Kazuko Inoue, Yasuo Yamaguchi, Haruhiro Hiraka, Toetsu Shishido, Hidef ...
2009 Volume 78 Issue 3 Pages
034602
Published: March 15, 2009
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Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiometric Heusler-type Ni
2.16Mn
0.78Ga
1.06 single crystal (conduction electron-to-atom ratio = 7.56). The splitting of a cubic (020) peak on a reciprocal lattice
c*-plane was traced with decreasing temperature from 400 to 37 K. It was found that an orthorhombic structure (
a>
b>
c) appears slightly below the transformation temperature as a metastable transient precursor structure before the formation of a final stable tetragonal structure (
a=
b<
c). The modes of deformation from cubic to orthorhombic are (i) simple shrinking and elongation of two cubic axes or (ii) a shuffling-like deformation along the cubic ‹110› direction on one of the cubic planes. The mode of deformation from orthorhombic to tetragonal is a shuffling-like deformation along the orthorhombic ‹110› direction on the orthorhombic
c-plane. Both shuffling-like deformations originate from tilting deformations that preserve the common ‹111› direction.
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Kenji Kodama, Ryoma Kokufu, Nobuyoshi Hosoito
2009 Volume 78 Issue 3 Pages
034701
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Element-specific magnetization processes in antiferromagnetically coupled ferro/ferri/ferromagnetic trilayer systems made of Fe/FeGd/Fe and Co/FeGd/Co were investigated by x-ray magnetic circular dichroism (XMCD) spectra and resonant x-ray magnetic reflectivity (RXMR). The magnetic field dependence of the RXMR intensities at the Gd
L3-absorption edge for the Fe/FeGd/Fe trilayer and that of the XMCD and RXMR intensities at the Gd
L3-, Fe
K-, and Co
K-absorption edges for the Co/FeGd/Co trilayer were measured. The element-specific magnetization processes of Gd moments with the in-plane applied field were compared between the Fe/FeGd/Fe and Co/FeGd/Co trilayers. The experimental results indicate that the Gd magnetization rotates either clockwise or anticlockwise with equal probability in the Co/FeGd/Co trilayer, whereas it rotates in one direction in the Fe/FeGd/Fe trilayer. The magnetic anisotropies along the in-plane directions were estimated for both trilayers from remanence measurements in various in-plane directions. We discuss the different rotation modes of the Gd magnetization in terms of the distribution of in-plane magnetic easy directions.
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Peng Tong, Yongsu Wu, Bongju Kim, Daeyoung Kwon, J. M. Sungil Park, Bo ...
2009 Volume 78 Issue 3 Pages
034702
Published: March 15, 2009
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This study compares the electrical resistivity, magnetization, and high-resolution neutron powder diffraction data obtained for Pr
0.5Ca
0.5CoO
3 and Pr
0.5Ca
0.5CoO
3−δ (δ∼0.045). Although both samples exhibit similar structural parameters, the distortion of the CoO
6 octahedra is weaker in Pr
0.5Ca
0.5CoO
3−δ than in Pr
0.5Ca
0.5CoO
3 at low temperatures. This reduced distortion decreases the electron–lattice coupling, which increases the itinerant nature of the
eg electrons in the oxygen-deficient sample. In addition, the oxygen deficiency can add Co
3+ ions into Pr
0.5Ca
0.5CoO
3−δ, yielding an increased population of
eg electrons. As a result, the sharp spin-state transition observed in Pr
0.5Ca
0.5CoO
3 is suppressed in Pr
0.5Ca
0.5CoO
3−δ, which exhibits a lower magnitude of resistivity and stronger magnetism at low temperatures.
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Hiroyuki Okazaki, Rikiya Yoshida, Takayuki Muro, Takanori Wakita, Masa ...
2009 Volume 78 Issue 3 Pages
034703
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We have performed high-resolution soft x-ray B 1
s core-level photoemission spectroscopy of heavily boron-doped diamond films in order to study the chemical sites of doped-boron atoms and their relation to the superconducting transition temperature (
Tc). We find that B 1
s core-level spectra exhibit several fine structures and three bulk components can be resolved from photon energy dependent studies and spectral fittings. These results indicate existence of several chemical environments of doped-boron atoms. One of the bulk components having the lowest binding energy can be assigned to a signal from substitutionally doped-boron atoms. Comparisons of bulk components with
Tc suggest spectroscopic evidence for the importance of substitutionally doped-boron atoms for effective carrier and superconductivity.
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Yoshinori Tabata, Noritaka Kuroda
2009 Volume 78 Issue 3 Pages
034704
Published: March 15, 2009
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The survival probability of solitons diffusing on a one-dimensional lattice with traps is studied numerically. Solitons are assumed to collapse once they collide with one another or reach traps. It turns out that, as the density of traps increases, the decay profile tends to change into an exponential-like form from an extremely nonexponential one specific to the geminate recombination on a trap-free lattice. The randomness of the distance between adjacent traps, as well as the disorder of the intersite energy barriers for the hopping motion of solitons, functions to reduce the deviation of the decay profile from that in the case of the trap-free lattice. Our calculation well reproduces the temperature-dependent decay profiles of the photoinduced neutral solitons that have been observed recently in the
MX-chain compound {[Pt(en)
2][Pt(en)
2Cl
2]}
3(CuCl
4)
4·12H
2O. It is suggested that traps are located at every 7 to 8 segments of the lattice and that the height of energy barriers is irregular to some extent. The periodicity of the valence of Cu ions is discussed on the basis of this result.
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Rikiya Yoshida, Hiroyuki Okazaki, Keisuke Iwai, Kengo Noami, Takayuki ...
2009 Volume 78 Issue 3 Pages
034705
Published: March 15, 2009
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We report the results of first photoemission spectroscopy on a newly discovered noncentrosymmetric superconductor Mg
10Ir
19B
16. We measured the valence band structure of Mg
10Ir
19B
16 using soft X-ray photoemission technique and found that the first principal calculation explains our observation well. In the bulk-sensitive laser-excited photoemission study, we observed that the intensity at the Fermi level decreases as we lower the sample temperature, indicative of the opening of superconducting energy gap. Using Dynes’ function, we performed fitting analysis on the spectra of superconducting state.
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Masayoshi Shimomoto, Yasutami Takada
2009 Volume 78 Issue 3 Pages
034706
Published: March 15, 2009
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By implementing diffusion Monte Carlo simulations as well as analyzing nonadiabatic processes perturbatively, we have made a detailed study of the properties of the ground state in a four-body Coulomb system (
M+M+m−m−) or a system composed of two holes and two electrons in an isotropic semiconductor with the mass ratio
m⁄
M in the range from 0.22 to 4.55 in which the adiabatic approximation cannot afford a bound state. We find that the attraction between
M+ particles induced by the nonadiabatic polarization of
m− particles (and
vice versa) is strong enough to bring about the bound ground state. On this basis, we propose the nonadiabatic mutual-polarization mechanism for biexciton formation.
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Shinya Tanikawa, Hiroyasu Matsuura, Kazumasa Miyake
2009 Volume 78 Issue 3 Pages
034707
Published: March 15, 2009
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Theory for temperature dependent valence of Sm ion in magnetically robust heavy fermion system SmOs
4Sb
12 is presented on the basis of the two-level (or double-well) Kondo model. It is shown that the conduction electrons with f-symmetry accumulate on the ion tunneling between double well potential when the temperature is decreased across the Kondo temperature.
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Rikiya Yoshida, Takanori Wakita, Hiroyuki Okazaki, Yoshikazu Mizuguchi ...
2009 Volume 78 Issue 3 Pages
034708
Published: March 15, 2009
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We have performed soft x-ray and ultrahigh-resolution laser-excited photoemission measurements on tetragonal FeSe, which was recently identified as a superconductor. Energy dependent study of valence band is compared to band structure calculations and yields a reasonable assignment of partial densities of states. However, the sharp peak near the Fermi level slightly deviates from the calculated energy position, giving rise to the necessity of self-energy correction. We have also performed ultrahigh-resolution laser photoemission experiment on FeSe and observed the suppression of intensity around the Fermi level upon cooling.
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Tsuneya Ando, Mikito Koshino
2009 Volume 78 Issue 3 Pages
034709
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Effects of electron–phonon interaction on the optical-phonon spectrum are studied within the lowest order perturbation in a bilayer graphene with potential difference associated with applied electric field. Due to the asymmetry of two layers, symmetric and antisymmetric modes are strongly mixed with each other and two peaks appear in Raman spectra. This behavior can also be controlled by a field due to an extra top gate. When the external field is sufficiently strong and opens up a gap comparable to the phonon energy, the phonons are modified considerably by resonant interband transitions.
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Kouhei Wakui, Satoshi Akutagawa, Naoki Kase, Kenji Kawashima, Takahiro ...
2009 Volume 78 Issue 3 Pages
034710
Published: March 15, 2009
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We report low-temperature specific heat measurements on the single-crystalline non-centrosymmetric superconductors T
2Ga
9 (T=Rh, Ir) with
Tc=1.95 and 2.25 K. Electronic contribution on the specific heat,
Cel, in each compound is well described by the BCS scheme, suggesting that both Rh
2Ga
9 and Ir
2Ga
9 fully open an isotropic gap in the superconducting state. The values of Δ
C⁄γ
Tc and 2Δ(0)⁄
kBTc indicate that both compounds are categorized as a weak coupling superconductor. The value of κ obtained from specific heat as a function of magnetic field strongly suggestes that T
2Ga
9 is a type-I superconductor.
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Shunsuke Tsuda, Takayoshi Yokoya, Takayuki Kiss, Takahiro Shimojima, K ...
2009 Volume 78 Issue 3 Pages
034711
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Noncentrosymmetric superconductors Li
2Pd
3B and Li
2Pt
3B are studied by high-resolution photoemission spectroscopy. The valence band spectra of Li
2Pd
3B and Li
2Pt
3B are well explained by first-principles band calculations. The sub-meV photoemission result shows that the size of the superconducting gap of Li
2Pd
3B is about 1.1 meV at 5.4 K with a reduced gap value (2Δ
0⁄
kBTc) of about 4.5, which is greater than the Bardeen–Cooper–Schrieffer (BCS) value of 3.52. The obtained superconducting gap can be explained more clearly with an
s-wave superconducting gap than with
p- and
d-wave superconducting gaps. This result indicates that Li
2Pd
3B is a conventional strong-coupling superconductor.
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Kiichi Miyazawa, Kunihiro Kihou, Parasharam M. Shirage, Chul-Ho Lee, H ...
2009 Volume 78 Issue 3 Pages
034712
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We have succeeded in synthesizing single-phase polycrystalline samples of oxygen-deficient oxypnictide superconductors,
LnFeAsO
1−y (
Ln: lanthanide elements) with
Ln=La, Ce, Pr, Nd, Sm, Gd, Tb, and Dy using high-pressure technique. It is found out that the synthesis pressure is a key parameter for synthesizing samples, in particular for the heavier
Ln’s, such as Tb and Dy. The lattice parameters systematically decrease with the atomic number of
Ln, reflecting the shrinkage of
Ln ionic radius. For the lighter
Ln’s (La, Ce, Pr, Nd),
Tc increases monotonously with decreasing the lattice parameters from 26 K for
Ln=La to 54 K for
Ln=Nd, then stays at the constant value around 53 K for the heavier counterpart (Nd, Sm, Gd, Tb, and Dy). The results suggest the intimate relationship between the crystal structural parameters and the superconductivity, as well as the possible existence of the inherent maximum
Tc, which is located around 50 K in the
LnFeAsO based materials.
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Ki-Seok Kim
2009 Volume 78 Issue 3 Pages
034713
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We propose one possible mechanism for deconfinement based on an SU(2) slave-boson theory. Resorting to an effective field theory approach, we show that introduction of an isospin interaction potential gives rise to a fermion zero mode in an instanton-hedgehog configuration. As a result, meron-type vortices are allowed. We demonstrate how emergence of such vortices results in the doping-independent decreasing ratio of superfluid weight.
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Yuuki Ota, Kiyohiro Sugiyama, Yuichiro Miyauchi, Yuji Takeda, Yasunori ...
2009 Volume 78 Issue 3 Pages
034714
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We succeeded in growing a high-quality single-crystal of CeAu
2Si
2, which was previously reported to be highly sample-dependent in terms of electrical and magnetic properties. CeAu
2Si
2 is not a simple AF1-type antiferromagnet, but reveals three antiferromagnetic transitions in a narrow temperature range from the Néel temperature
TN1=9.6 K to
TN3=8.0 K. A clear metamagnetic transition with two steps was observed at
Hc1=53 kOe and
Hc2=55 kOe in the magnetization curve below 5 K for the magnetic field along an antiferromagnetic easy-axis, namely, the tetragonal [001] direction, with a saturation moment of 1.53 μ
B/Ce. The magnetic susceptibility and magnetization are anisotropic, which are well explained by results of crystalline electric field analyses. We also studied the de Haas–van Alphen (dHvA) effect. The detected dHvA branches are found to be consistent with those of a non-4
f reference compound such as YCu
2Si
2.
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Youichi Yanase, Naoyuki Yorozu
2009 Volume 78 Issue 3 Pages
034715
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Motivated by the discovery of superconductivity in boron-doped (B-doped) diamond, we investigate the localization and superconductivity in heavily doped semiconductors. The competition between Anderson localization and
s-wave superconductivity is investigated from the microscopic point of view. The effect of microscopic inhomogeneity and the thermal fluctuation in superconductivity are taken into account using the self-consistent 1-loop-order theory with respect to superconducting fluctuation. The crossover from superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. We show that superconductor–insulator transition (SIT) accompanies the crossover. We point out an enhancement of Cooper pairing in the crossover regime. Further localization of the electron wave function gives rise to incoherent Cooper pairs and the pseudogap above
Tc. A global phase diagram is drawn for host band superconductivity, impurity band superconductivity, Anderson localization, Fermi liquid state, and pseudogap state. A theoretical interpretation is proposed for superconductivity in the doped diamond, SiC, and Si.
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Takuji Nomura
2009 Volume 78 Issue 3 Pages
034716
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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The high-transition-temperature (high-
Tc) superconductivity discovered recently in iron pnictides is analyzed within a perturbation theory. Specifically, the probable pairing symmetry, the doping dependence of the transition temperature and the pairing mechanism are studied by solving the Eliashberg equation for multi-band (2- and 5-band) Hubbard models with realistic electronic structures. The effective pairing interaction is expanded perturbatively in the on-site Coulomb integrals up to third order. Our perturbative weak-coupling approach shows that sufficiently large eigenvalues of the Eliashberg equation are obtained to explain the actual high transition temperatures by taking realistic on-site Coulomb integrals in the 5-band model. Thus, unconventional (non-phonon-mediated) superconductivity is highly likely to be realized. The superconducting order parameter does not change its sign on the Fermi surfaces, but it does change between the electron and hole Fermi surfaces. Consequently, the probable pairing symmetry is always “a nodeless extended
s-wave symmetry (more specifically, an
s±-wave symmetry)” over the whole parameter region that we investigated. It is suggested that the 2-band model is insufficient to explain the high values of
Tc.
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Yositake Takane, Shingo Iwasaki, Yuka Yoshioka, Masayuki Yamamoto, Kat ...
2009 Volume 78 Issue 3 Pages
034717
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We study the conductance of phase-coherent disordered quantum wires focusing on the case in which the number of conducting channels is imbalanced between two propagating directions. If the number of channels in one direction is by one greater than that in the opposite direction, one perfectly conducting channel without backscattering is stabilized regardless of wire length. Consequently, the dimensionless conductance does not vanish but converges to unity in the long-wire limit, indicating the absence of Anderson localization. To observe the influence of a perfectly conducting channel, we numerically obtain the distribution of conductance in both cases with and without a perfectly conducting channel. We show that the characteristic form of the distribution is notably modified in the presence of a perfectly conducting channel.
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Hiroyuki Kimura, Shuichi Wakimoto, Mamoru Fukunaga, Yukio Noda, Koji K ...
2009 Volume 78 Issue 3 Pages
034718
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Microscopic magnetic properties under the application of a magnetic field were investigated in multiferroic ErMn
2O
5 using neutron diffraction. Below
T=8 K upon applying a magnetic field along the
c-axis, an incommensurate–commensurate–incommensurate magnetic phase transition occurred. On the contrary, when the magnetic field was applied parallel to the
a-axis, no phase transition occurred up to
H=5 T.
H–
T phase diagrams obtained in the present study show a one-to-one correspondence with
H–
T phase diagrams for previously obtained dielectric properties, indicating that the field-induced dielectric transition was triggered by magnetic phase transition. The contrastive phase diagram between
H||
c and
H||
a suggests that the induced Er
3+ magnetic moment contributed significantly to the magnetic and dielectric responses to the magnetic field.
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Junya Otsuki, Hiroaki Kusunose, Yoshio Kuramoto
2009 Volume 78 Issue 3 Pages
034719
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Magnetic and charge susceptibilities in the Kondo lattice are derived by the continuous-time quantum Monte Carlo (CT-QMC) method combined with the dynamical mean-field theory. For a weak exchange coupling
J and near half filling of the conduction band, antiferromagnetic transition occurs as signalled by divergence of the staggered magnetic susceptibility with lowering temperature. With increasing
J, the Kondo effect suppresses the divergence, and the critical value of
J agrees well with Doniach’s estimate which considers the RKKY interaction as competing with the Kondo effect. For low density of conduction electrons, a ferromagnetic ordering is observed where Doniach’s estimate does not work. Around quarter filling, a charge-density-wave (CDW) transition is found. The CDW is interpreted from the strong-coupling limit in terms of effective repulsion between Kondo singlets.
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Xing-Lai Che, Jia-Hao Li, Ye Dai, Bai-Xin Liu
2009 Volume 78 Issue 3 Pages
034720
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Based on the projector augmented-wave method,
ab initio calculations are performed for 20 representative binary Ni–Au, Ni–Cu, Ni–Zn, and Ni–Al alloys at A
3B composition. The calculations reveal that the D0
22 Ni
3Au, Ni
3Cu, Ni
3Zn, and L1
2 Ni
3Al are more energetically stable than their respective competitive structures, indicating that the four structures may be formed in some appropriate conditions. The calculations indicate that different structures have small effects on the magnetic moments for Ni
3Au and Ni
3Cu alloys, while have large effects on the magnetic moments for Ni
3Zn and Ni
3Al alloys. It is also predicted that there is strong hybridization between Ni 3d and Cu 3d states in Ni
3Cu and Ni 3d and Au 5d states in Ni
3Au alloys and little hybridization in Ni
3Al and Ni
3Zn, which may significantly affect on structural stability and magnetism of these structures. The calculations suggest that the magnetism may increase the energetic stability of these structures. It is hoped that these interesting finding would stimulate further experimental investigations on the binary metastable Ni–Au (Cu, Zn, Al) intermetallics.
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Bal Krishna Agrawal, Ashish Pathak, Savitri Agrawal
2009 Volume 78 Issue 3 Pages
034721
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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A detailed comprehensive
ab-initio study of the structural, electronic and optical properties of the unpassivated and H-passivated SiC nanowires (NWs) grown along [001] direction having diameters lying in the range, 3.35 to 15.42 Å has been made by employing the first-principles pseudopotential method within density functional theory (DFT) in the generalized gradient approximation (GGA). We investigate two types of the NWs having hexagonal and triangular cross-sections. The binding energy (BE) increases with the diameter of the NW because of decrease in the relative number of the unsaturated surface bonds. The band gap decreases with the diameter of the NW because of the quantum confinement. After atomic relaxation, appreciable distortion occurs in the NWs where the chains of Si- and C-atoms are curved in different directions. These distortions are reduced with the diameters of the NWs. The different NWs reveal different electronic properties, e.g., one NW is seen to be metallic whereas the other one is semi-metallic and the remaining NWs are semiconducting. The optical absorption is quite strong in the ultraviolet (UV) region but is quite appreciable in the visible and infrared (IR) regions. Thus, the NWs may have applications in the development of the devices emitting right from IR to UV electromagnetic radiations.
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Tohru Aonuma, Yuki Fuseya, Masao Ogata
2009 Volume 78 Issue 3 Pages
034722
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We report on the result of quantum Monte Carlo simulation of quasi-one-dimensional electron systems at 1/4-filling, considering organic superconductors such as TMTSF- and TMTTF-salts. We focus on the effect of dimensionality (interchain coupling) on superconducting fluctuation. First we consider Hubbard model which includes only on-site repulsion
U. We find that the increase of interchain coupling enhances superconducting susceptibility, although the interchain hopping deforms the nested Fermi surface and suppresses the spin susceptibility. The obtained results for the superconductivity in the Hubbard model show qualitative agreement with recent renormalization group studies, and have the possibility of accounting for the recent experimental result of (TMTTF)
2SbF
6, whose transition temperature increases by applying pressure. Next we consider an extended Hubbard model which includes nearest-neighbor repulsion
V. In this case we consider the competition between different symmetries of electron pairing,
dx2−y2- and
dxy-wave symmetry, and find that the particle–particle interaction vertex for
dx2−y2-wave pairing is no longer attractive even in the region where nesting condition still holds. On the other hand, the interaction vertex for
dxy-wave pairing persists to be attractive: This means that the
dx2−y2- and
dxy-wave superconductivity compete with each other even if
V is small. We clarify the qualitative difference in the effect of dimensionality between the
dx2−y2-wave superconductivity.
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Tadashi Fukuhara, Ryoichi Yamagata, Lingwei Li, Katsuhiko Nishimura, K ...
2009 Volume 78 Issue 3 Pages
034723
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We have investigated the specific heat and transport properties of the new ferromagnetic compound Nd
3Al with the hexagonal Ni
3Sn structure. At low temperatures well below the Curie temperature of 74 K, the temperature dependence of specific heat and electrical resistivity are consistently explained by considering the influence of magnon excitation with an anisotropy gap of about 30 K. An unexpected enhancement of the specific heat coefficient, γ∼42 mJ/(mol·K
2) is observed. In the ferromagnetically ordered state, the predominant contribution of the term proportional to the square of resistivity to the anomalous Hall resistivity is observed. Thermoelectric power changes its sign from negative to positive at around 60 K with increasing temperature.
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Eiichi Matsuoka, Shoei Ogushi, Yuta Sasaki, Masato Sakata, Kenji Ohoya ...
2009 Volume 78 Issue 3 Pages
034724
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Gd substitution for Dy in DyB
2C
2 that undergoes an antiferroquadrupolar (AFQ) ordering at
TQ=24.7 K and an antiferromagnetic (AFM) one at
TN=15.3 K enhances the AFM interaction and weakens the AFQ interaction. In Dy
0.8Gd
0.2B
2C
2, the AFQ transition occurs at
TQ=17.6 K below the AFM one at
TN=19.0 K. However, the strong competition between the AFQ and AFM interactions supresses the development of the AFQ order parameter below
TQ and causes an anomalous behavior in field-induced transitions. The magnetic phase diagrams of Dy
0.8Gd
0.2B
2C
2 drawn from the experimental results of specific heat and magnetization have anomalous phase boundaries originating from this competition.
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Kozo Okada
2009 Volume 78 Issue 3 Pages
034725
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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The electronic structures of Nd
2−xCe
xCuO
4 and La
2−xSr
xCuO
4 are studied using numerical diagonalization calculations for cluster models, Cu
5O
16, Cu
7O
20, and Cu
8O
16. The Fermi energy of Nd
2CuO
4 used in the experiment is assumed to be pinned at the bottom of the upper Hubbard band, while that of La
2CuO
4 is assumed to be pinned at the top of the Zhang–Rice singlet band. This assumption enables us to consistently understand the doping dependence of the Cu 2
p photoemission and photoabsorption spectra in Nd
2−xCe
xCuO
4 and La
2−xSr
xCuO
4 on the basis of the so-called “crossing the gap” picture. The present calculation of Cu 2
p photoemission spectrum also shows that core hole screening caused by charge transfer between neighboring CuO
4 plaquettes, in other words, nonlocal screening (NLS), is important in Nd
2CuO
4 as well as in La
2CuO
4.
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Petter Holme
2009 Volume 78 Issue 3 Pages
034801
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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Many real-world networks have broad degree distributions. For some systems, this means that the functional significance of the vertices is also broadly distributed, in other cases the vertices are equally significant, but in different ways. One example of the latter case is metabolic networks, where the high-degree vertices — the currency metabolites — supply the molecular groups to the low-degree metabolites, and the latter are responsible for the higher-order biological function, of vital importance to the organism. In this paper, we propose a generalization of currency metabolites to currency vertices. We investigate the network structural characteristics of such systems, both in model networks and in some empirical systems. In addition to metabolic networks, we find that a network of music collaborations and a network of e-mail exchange could be described by a division of the vertices into currency vertices and others.
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Shuhei Takao, Tatsuyuki Eguchi, Hirohide Yata, Kaoru Shoda, Satoshi Ic ...
2009 Volume 78 Issue 3 Pages
034802
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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SiC particles that are covered with projections and have a porous inner substructure are grown via metal organic chemical vapor deposition using methylvinyldichlorosilane as the source material and Fe catalyst on the Si substrate. Electron microscopy reveals that a SiC particle is located at the tip of a nanowire indicating that a SiC particle is formed at the final stage of a metal-mediated growth of a nanowire. A catalyzed ballistic deposition model is proposed to explain the growth of the particles.
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Jae-Suk Yang, Seungbyung Chae, Wooseop Kwak, Sun-Bin Kim, In-mook Kim
2009 Volume 78 Issue 3 Pages
034803
Published: March 15, 2009
Released on J-STAGE: December 28, 2011
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We conceptualize knowledge as an intellectual infrastructure that helps to maximize efficiency from the viewpoint of ecosystems. The knowledge ecosystem includes people and organizations that participate in the production, distribution, and consumption of this knowledge and information, as well as interactions between participants. We built the agent-based computational model of the ecosystem and induced seven key revitalization conditions from the perspective of complexity science and ecosystem management. We analyzed the effects of these conditions on the knowledge ecosystem based by the simulation of the agent-based model. Our results suggest that the proper implementation of seven revitalization conditions, focusing on the recovery of the positive feedback loop in the knowledge ecosystem, is crucial for sustainable development.
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