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Tatsuro Yuge, Akira Shimizu
2007 Volume 76 Issue 9 Pages
093001
Published: September 15, 2007
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The long-time behavior of the velocity autocorrelation function (VACF) is investigated by the molecular dynamics simulation of a two-dimensional system which has both a many-body interaction and a random potential. With strengthening the random potential by increasing the density of impurities, a crossover behavior of the VACF is observed from a positive tail, which is proportional to
t−1, to a negative tail, proportional to −
t−2. The latter tail exists even when the density of particles is the same order as the density of impurities. The behavior of the VACF in a nonequilibrium steady state is also studied. In the linear response regime the behavior is similar to that in the equilibrium state, whereas it changes drastically in the nonlinear response regime.
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Ju Hyun Park
2007 Volume 76 Issue 9 Pages
093002
Published: September 15, 2007
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This letter deals with the synchronization of discrete-time chaotic systems. Based on the Lyapunov method, we present a new control method that guarantees that the synchronized states are asymptotically stable. The controller consists of two parts: one is a linear dynamic controller, and the other is a nonlinear control law for compensating the nonlinear terms of the error signal. Then, the existence criterion of the controller for the synchronization is derived. The criterion is expressed as a linear matrix inequality (LMI), readily solvable by various convex optimization algorithms.
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Takao M. Kojima, Dai Tomono, Tokihiro Ikeda, Katsuhiko Ishida, Yoshio ...
2007 Volume 76 Issue 9 Pages
093501
Published: September 15, 2007
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We have demonstrated that the beam density of 54 MeV/
c muons can be increased almost by a factor of two when a tapered glass tube is inserted coaxially along the muon beam. The observations are compared with a multiple Coulomb scattering calculation, which reproduces the observation reasonably. This technique opens a new and simple way to increase the muon intensity effectively.
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Akihiro Sakai, Fumiyuki Ishii, Yoshinori Onose, Yasuhide Tomioka, Sato ...
2007 Volume 76 Issue 9 Pages
093601
Published: September 15, 2007
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We study, both experimentally and theoretically, temperature and electron-density (band-filling) dependence of Seebeck coefficient in B20-type transition-metal monosilicides to critically study the validity of the Boltzmann transport theory based on the band structure as a guiding principle for the materials design of metallic thermoelectric compounds. The global thermoelectric phase diagram for a wide range of materials (CrSi–MnSi–FeSi–CoSi–Co
0.85Ni
0.15Si and their interpolating solid solutions) is obtained. Theoretical results derived from the calculated band structure can reproduce a global feature of experimental results except the higher temperature region of FeSi, providing the firm basis to understand the systematics of thermoelectricity in metallic compounds including the role of electron correlation and to develop the material design for larger thermoelectricity.
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Yuki Fuseya, Masao Ogata
2007 Volume 76 Issue 9 Pages
093701
Published: September 15, 2007
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Response functions for spin-density-wave (SDW) and
d-wave singlet superconductivity (
dSC) in quasi-one-dimensional (Q1D) electron systems are calculated by a renormalization group technique. It is shown that the response functions for both SDW, χ
s, and
dSC, χ
d, are enhanced by interchain hopping,
t⊥, i.e., by quasi-one dimensionality. When the Fermi surface deviates from perfect nesting, χ
s saturates below the energy scale of imperfectness of the nesting, while χ
d is hardly affected. Consequently, the superconducting correlation increases even away from the SDW phase. This gives a possible interpretation of the recent experimental results of Q1D organic conductor (TMTTF)
2SbF
6, where
Tc increases even away from the SDW phase.
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Keitaro Kuwahara, Kazuaki Iwasa, Masahumi Kohgi, Naofumi Aso, Masafumi ...
2007 Volume 76 Issue 9 Pages
093702
Published: September 15, 2007
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We have performed a single crystal neutron scattering experiment on Ce
0.7La
0.3B
6 to microscopically investigate the order parameter of phase IV. Below the phase transition temperature 1.5 K of phase IV, weak but distinct superlattice reflections at the scattering vector
κ=(
h⁄2,
h⁄2,
l⁄2) (
h,
l=odd number) have been observed for the first time by neutron scattering. The intensity of the superlattice reflections is stronger for high scattering vectors, which is quite different from the usual magnetic form factor of magnetic dipoles. This result directly evidences that the order parameter of phase IV has a complex magnetization density, consistent with the recent experimental and theoretical prediction in which the order parameter is the magnetic octupoles
Tβ with Γ
5 symmetry of the point group
Oh. Neutron scattering experiments using short wavelength neutrons, as done in this study, could become a general method to study the high-rank multipoles in f electron systems.
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Eiichi Negishi, Shun Yabuta, Naoki Toyota, Takuya Matsumoto, Toyonari ...
2007 Volume 76 Issue 9 Pages
093703
Published: September 15, 2007
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We have measured the dielectric response as a function of both frequency (
f=0.3 Hz–100 kHz) and electric bias field for a quasi-one-dimensional, polar conductor (EDT-TTFVO)
2FeBr
4 undergoing a ferrimagnetic-like transition at
TC∼0.9 K. Around
T*=15 K, the dielectric constant at low
f exhibits a peak that shifts to higher
T at higher
f, being reminiscent of relaxor ferroelectrics with glassy polarizations. Since this dielectric anomaly is also present in the nonmagnetic isostructural GaBr
4 salt, the polarizations may be ascribed to both π and σ electrons localized on the polar donor. At
TC<
T<7 K, the complex dielectric constant clearly exhibits a Debye relaxation, and the relaxation time follows a critical behavior as (
T−
T0)
−nτ (
nτ=6.5) toward
T0=0.75±0.15 K just very close to
TC. This phenomenon of the dielectric-slowing-down toward the magnetically ordered state is discussed as a novel type of multifunctional coupling in the short-range ordered state between the possible electric polarization in the distorted tetrahedral anion and the centered
d spin of 5/2, the latter of which, eventually at
TC, may induce the magnetic order with π spins of 1/2 disproportionately localized on the polar donors.
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Takahiro Namiki, Yuji Aoki, Hideyuki Sato, Chihiro Sekine, Ichimin Shi ...
2007 Volume 76 Issue 9 Pages
093704
Published: September 15, 2007
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We report on a systematic study of the superconducting characteristics and Pr crystalline-electric-field (CEF) levels of the filled skutterudite PrRu
4As
12 (
Tc=2.33 K). The temperature dependences of the upper critical field
Hc2 and the Ginzburg–Landau (Maki) parameter κ
2 suggest
s-wave clean-limit superconductivity. The electronic specific heat coefficient γ∼95 mJ/(K
2·mol), which is ∼1.5 times larger than that of LaRu
4As
12, indicates 4
f-originating quasiparticle mass enhancement. The magnetic susceptibility χ(
T) indicates that the CEF ground state is a Γ
1 singlet and a Γ
4(1) triplet first excited state lies at Δ
CEF∼30 K above. A systematic comparison among PrOs
4Sb
12, PrRu
4Sb
12, PrRu
4As
12, and La-based reference compounds suggests that the inelastic exchange scattering and aspherical charge scattering of conduction electrons from CEF-split 4
f levels play an essential role in the quasiparticle mass enhancement and in determining the value of
Tc in the Pr-based filled skutterudites.
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Yasukage Oda, Hiroaki Takezoe, Aya Tamura, Gaku Motoyama, Eiji Sakagam ...
2007 Volume 76 Issue 9 Pages
093705
Published: September 15, 2007
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TiCo, a d-band metal, is known to be an exchange-enhanced itinerant paramagnet. We measured the dc susceptibility of polycrystalline Ti
0.5+xCo
0.5−x with small
x over the temperature range of 1.7 to 300 K. In order to study superconductivity, the ac susceptibility of this compound was also measured down to 14 mK. We observed superconductivity in this system, whose superconducting transition temperature was approximately 35 mK for Ti
0.510Co
0.490.
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Atsushi Kitada, Zenji Hiroi, Yoshihiro Tsujimoto, Taro Kitano, Hiroshi ...
2007 Volume 76 Issue 9 Pages
093706
Published: September 15, 2007
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A quasi-two-dimensional
S=1⁄2 Heisenberg square-lattice antiferromagnet (CuCl)LaNb
2O
7 is studied by specific heat and magnetic susceptibility measurements in external fields up to 14 T. The experimental results in low fields verify the absence of the order–disorder transition, as reported previously. By further application of magnetic fields, we obtain direct evidence for the phase transition, which can be interpreted as the Bose–Einstein condensation (BEC) of magnons. However, the critical field of 10 T significantly deviates from that estimated from the zero-field gap, indicating that, unlike known experimental examples, the one-magnon mode is
not a primary source to drive the BEC.
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Masashi Fujinaga, Naomichi Hatano
2007 Volume 76 Issue 9 Pages
094001
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We investigate the entanglement of the ferromagnetic
XY model in a random magnetic field at zero temperature and in the uniform magnetic field at finite temperatures. We use the concurrence to quantify the entanglement. We find that, in the ferromagnetic region of the uniform magnetic field
h, all the concurrences are
generated by the random magnetic field and by the thermal fluctuation. In one particular region of
h, the next-nearest neighbor concurrence is generated by the random field but not at finite temperatures. We also find that the qualitative behavior of the maximum point of the entanglement in the random magnetic field depends on whether the variance of its distribution function is finite or not.
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Atsushi Nagai, Yoshinori Kametaka
2007 Volume 76 Issue 9 Pages
094002
Published: September 15, 2007
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Two linear fractional differential equations appearing in the field of fluid mechanics are investigated. These equations are solved by employing a Puiseux expansion and their solutions are expressed in terms of the Mittag–Leffler function. Ordinary differential equations without fractional derivatives that the fundamental solutions satisfy are also derived. We also present an integrable discretization of the fractional differential equation together with its solution.
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Masafumi Kaga, Takao Ohta
2007 Volume 76 Issue 9 Pages
094003
Published: September 15, 2007
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We study the shrinkage dynamics of a vesicle out of equilibrium. In our previous paper, we introduced a kinetic theory of a vesicle interacting with surfactant molecules. In the present paper, we extend the theory to cover more variety of chemical reactions. It is shown that the chemical kinetics change drastically the relation between the waiting time of pore formation and the radius of vesicle. Numerical simulations are carried out to confirm our analytical results.
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Sumio Wada
2007 Volume 76 Issue 9 Pages
094004
Published: September 15, 2007
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We present an alternative frequentists’ proof of the quantum probability rule which does not make use of the frequency operator, with expectation that this can circumvent the recent criticism against the previous proofs which use it. We also argue that avoiding the frequency operator is not only for technical merits for doing so but is closely related to what quantum mechanics is all about from the viewpoint of many-world interpretation.
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Chiyori Urabe
2007 Volume 76 Issue 9 Pages
094401
Published: September 15, 2007
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We investigate the formation processes of a sandpile using numerical simulation. We find a new relation between the fluctuation of the motion of the top and the surface state of a sandpile. The top moves frequently as particles are fed one by one every time interval
T. The time series of the top location has the power spectrum which obeys a power law,
S(
f)∼
fα, and its exponent α depends on
T and the system size
w. The surface state is characterized by two time scales; the lifetime of an avalanche,
Ta, and the time required to cause an avalanche,
Ts. The surface state is fluid-like when
Ta∼
Ts, and it is solid-like when
Ta<<
Ts. Our numerical results show that α is a function of
Ts⁄
Ta.
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Sebastian Popescu, Yasunori Ohtsu, Hiroharu Fujita
2007 Volume 76 Issue 9 Pages
094501
Published: September 15, 2007
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The spatial profiles of the plasma potential at the crest and the trough phases of the oscillating radio-frequency field in an inductively coupled plasma, in uniform magnetic field, were obtained from the first derivative of the time-averaged current–voltage characteristics of an axially movable emissive probe. On this basis the axial profile of the time-averaged plasma potential was evaluated, it confirming the existence of an electric double layer inside the plasma source. The oscillation amplitude of the plasma potential was obtained as well, it being a measure of the axial component of the excited magnetic field amplitude. Moreover, the oscillation amplitude profile shows a high sensitivity to the presence of the double layer inside the plasma, it having a pronounced maximum at the location of the above space charge structure.
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Hiroshi Abe
2007 Volume 76 Issue 9 Pages
094601
Published: September 15, 2007
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An expansion of a pair-correlation function is introduced to express medium-rage order (MRO). The approximated correlation function is extended from conventional short-range order (SRO) parameters. SRO parameters are obtained by the conditional average of a pair-correlation function. It is demonstrated that the model can reconstruct SRO and MRO of atomic arrangements from an initial random state by Monte Carlo (MC) method. MRO parameters control cluster formations such as heterogeneous microstructures. On an approach of atomic pair- and triplet-interactions, approximated many-body interactions are estimated in the simulations. Moreover, the MC simulations are applied to ordering process on cooling in Ag
xTiS
2 regarded as a typical two-dimensional material. Furthermore, cluster developments are visualized by the reverse MC method.
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Go Watanabe, Yuka Tabe
2007 Volume 76 Issue 9 Pages
094602
Published: September 15, 2007
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Hydrophobic compounds of smectic liquid crystals are spontaneously spread on a liquid surface to form softly-condensed monomolecular films. The constituent molecules are coherently tilted from the surface normal when they form smectic-C phase in the bulk state, while the molecules are aligned perpendicular to the surface when they form smectic-A or -B phase in the bulk. The result proves that the tilting property in the smectic liquid crystals should be determined only by the intralayer molecular interaction. The molecular dynamics simulations can reproduce the experimental result satisfactorily and also suggest that the molecular dipole moment should play an essential role to cause the coherent molecular tilt in smectic liquid crystals.
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Kazumasa Hattori, Kazumasa Miyake
2007 Volume 76 Issue 9 Pages
094603
Published: September 15, 2007
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The physical origin of frequency dependence in elastic constants, which are often found in an ultrasound propagation in filled skutterudites and clathrate compounds, is investigated theoretically. This dependence arises from a coupling between the acoustic phonon and some optical phonons, which strongly interact with electrons. Using a self-consistent ladder approximation together with a pseudofermion mapping of the phonon to the single site Holstein Anderson model, a soft mode of the optical phonon at zero frequency is shown to emerge. The temperature dependence of the spectral weight of this soft mode shows an activation-type behavior, which is characterized by the optical phonon frequency. These features can generate the frequency dependence and the shoulder in the elastic constants observed in some filled skutterudites and clathrate compounds.
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Motohiko Ezawa
2007 Volume 76 Issue 9 Pages
094701
Published: September 15, 2007
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The intrinsic Zeeman energy is precisely one half of the cyclotron energy for electrons in graphene. As a result a Landau-level mixing occurs to create the energy spectrum comprised of the 4
j-fold degenerated zero-energy level and 4-fold degenerated nonzero-energy levels in the
j-layer graphene, where
j=1,2,3 for monolayer, bilayer and trilayer, respectively. The degeneracy manifests itself in the quantum Hall (QH) effect. We study how the degeneracy is removed by the Coulomb interactions. With respect to the zero-energy level, an excitonic gap opens by making a BCS-type condensation of electron–hole pairs at the filling factor ν=0. It gives birth to the Ising QH ferromagnet at ν=±1 for monolayer, ν=±1,±3 for bilayer, and ν=±1,±3,±5 for trilayer graphene from the zero-energy degeneracy. With respect to the nonzero-energy level, a remarkable consequence is derived that the effective Coulomb potential depends on spins, since a single energy level contains up-spin and down-spin electrons belonging to different Landau levels. The spin-dependent Coulomb interaction leads to the valley polarization at ν=±4,±8,±12,… for monolayer, ν=±2,±6,±10,… for bilayer, and ν=±2,±4,±8,±12,… for trilayer graphene.
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Ryousuke Shiina, Osamu Sakai, Hiroyuki Shiba
2007 Volume 76 Issue 9 Pages
094702
Published: September 15, 2007
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Elastic neutron scattering spectra expected for ordered magnetic octupoles are studied theoretically for Ce
1−xLa
xB
6 and NpO
2. Assuming the order parameter deduced from the resonant X-ray scattering and NMR experiments, we have calculated spin and orbital parts of the magnetic form factors using the radial wave function for the single
f-electron state in the Ce and Np ions. The octupolar contributions to the form factor at the superlattice spots are shown to be quite small in the long wave-length region, whereas it becomes markedly enhanced for short wave lengths. We discuss how and to what extent the intensity due to octupoles in short wave length is developed, and whether it is observable in experiments. The anisotropy of the form factor is discussed in connection with the symmetry aspect of the neutron cross section due to octupoles. In the case of Ce
1−xLa
xB
6, it is shown that the calculated results are consistent with recent observations by Kuwahara
et al., thus confirming for the first time the existence of the ordered octupole by neutron scattering.
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Takashi Nakajima, Takeji Ueda, Susumu Komiyama
2007 Volume 76 Issue 9 Pages
094703
Published: September 15, 2007
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The quantum Hall plateau-to-insulator (plateau) transition is studied in small GaAs two-dimensional electron gas systems, where the system size
L is comparable to or smaller than the correlation length
Lcor of potential fluctuation. At low temperatures, the transition depends on the system size but the dependence is not explained in terms of Anderson localization. At elevated temperatures, the transition width exhibits a power-law dependence but the exponent κ takes nonuniversal values. It is suggested that the transition crosses over from the well-known, Anderson localization dominated regime to the semiclassical percolation-dominated regime when the system size is reduced below
Lcor.
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Hanako Isshiki, Denis Konstantinov, Hikota Akimoto, Keiya Shirahama, K ...
2007 Volume 76 Issue 9 Pages
094704
Published: September 15, 2007
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We have investigated the intersubband transitions of surface-state electrons (SSE) on liquid
3He induced by microwave radiation at temperatures from 1.1 K down to 0.01 K. Above 0.4 K, the transition linewidth is proportional to the density of
3He vapor atoms. This proportionality is explained well by Ando’s theory, in which the linewidth is determined by the electron–vapor atom scattering. However, the linewidth is larger than the calculated result by a factor of 2.1. This discrepancy strongly indicates that the theory underestimates the electron–vapor atom scattering rate. At lower temperatures, the absorption spectrum splits into several peaks. The multiple-peak structure is partly attributed to the spatial inhomogeneity of the static holding electric field perpendicular to the electron sheet.
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Sogo Kuroiwa, Yoko Tomita, Akira Sugimoto, Toshikazu Ekino, Jun Akimit ...
2007 Volume 76 Issue 9 Pages
094705
Published: September 15, 2007
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We report on magnetic, transport, specific heat and tunneling measurements of NbB
2 with the maximum superconducting critical temperature
Tc∼10 K. The essential superconducting properties have been investigated through mapping out the critical field phase diagram, from which it is turned out to be type II superconductor with a small Ginzbrug–Landau parameter κ∼2.2. Both the tunneling and specific heat measurements indicate that our NbB
2 specimen has a single gap and
s-wave pairing symmetry with a weak-coupling limit. The electron–phonon coupling constant is estimated to be λ
ep=0.71±0.02, suggesting that the maximum
Tc of NbB
2 can be explained by the McMillan formula.
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Shinji Kouno, Naoki Shirakawa, Ichiro Nagai, Norio Umeyama, Kazuyasu T ...
2007 Volume 76 Issue 9 Pages
094706
Published: September 15, 2007
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Sr
3Mo
2O
7 is a member of the Ruddlesden–Popper type series of Sr
n+1Mo
nO
3n+1 with
n=2, a so-called double layered perovskite. We have successfully synthesized polycrystalline samples of single-phase Sr
3Mo
2O
7 with the aid of Ti
2O
3 as
p(O
2) buffer. The phase-pure samples allowed us to perform measurements of the electrical resistivity and the magnetic susceptibility on Sr
3Mo
2O
7 for the first time. The resistivity revealed that Sr
3Mo
2O
7 is a metallic conductor from 300 K to 30 mK. The Pauli-paramagnetic behavior is observed in the susceptibility. This means that Sr
n+1Mo
nO
3n+1 for
n=1, 2, and ∞ all show the Pauli-paramagnetic metal behavior, in contrast to Sr
n+1Ru
nO
3n+1 of an electronic analogue series.
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Hirotaka Sano, Akira Endo, Shingo Katsumoto, Yasuhiro Iye
2007 Volume 76 Issue 9 Pages
094707
Published: September 15, 2007
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Superconducting wire network subjected to a uniform and a checkerboard-patterned magnetic field is investigated. The checkerboard field is created by an array of ferromagnetic dots placed on top of the superconducting network. Measurements of the current–voltage (
I–
V) characteristics have revealed the canonical Kosterlitz–Thouless–Berezinskii (KTB) transition at zero magnetic field. The superconducting transition at α=1⁄2 (α being the frustration parameter) is studied in detail, and compared with the theoretical predictions on the fully frustrated XY model which has a double degeneracy in the ground state vortex configuration. The
I–
V characteristics for α=1⁄2 is consistent with the scenario of kink–antikink unbinding at antiphase domain boundaries first proposed by Korshunov [Phys. Rev. Lett.
88 (2002) 167007]. Introduction of the checkerboard field with amplitude β to the α=1⁄2 case lifts the double degeneracy. The effect of non-zero β on the nature of superconducting transition at α=1⁄2 is consistent with this picture. The KTB transition is restored at β=1⁄2.
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Atsutaka Maeda, Haruhisa Kitano, Kentaro Kinoshita, Terukazu Nishizaki ...
2007 Volume 76 Issue 9 Pages
094708
Published: September 15, 2007
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The effects of Zn impurities on the electronic state in the vortex core were investigated systematically in almost optimally doped YBa
2(Cu
1−xZn
x)
3O
y (0≤
x≤0.06) using the microwave complex surface impedance (
Zs) measurement technique. We estimated the viscosity, η, and the pinning constant, κ
p, of a vortex as functions of temperature and
x on the basis of a mean-field theory of the vortex motion. κ
p as a function of Zn concentration,
x, suggests that Zn doping is not an effective procedure for pinning the vortex motion. η(
x) depended very weakly on
x for
x≤0.003, while it decreased rapidly with increasing
x for
x>0.003. These finding suggest that the scattering of QPs in the vortex core is much larger than that in the Meissner (zero-field) state for
x≤0.003. On the other hand, for
x>0.003, the scattering of QPs in the vortex core is governed by Zn impurity, showing that the presence of the vortex is not important for the scattering in this regime. The large scattering in the low-doping-concentration region (
x≤0.003) is particularly important, since this is characteristic of the presence of the vortex core. Our result is consistent with the previously published microwave result for the Zn-free material [Tsuchiya
et al.: Phys. Rev. B
63 (2001) 184517] in the sense that both experimental data suggest the existence of the high QP-DOS in the vortex core, but is inconsistent with a picture proposed by STM measurements on the vortex core. We discuss possible origins for this discrepancy, including novel mechanisms of energy dissipation in the motion of a moderately clean (
l∼ξ) vortex core.
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Hiroyuki Mitamura, Setsuo Mitsuda, Shunsuke Kanetsuki, Hiroko Aruga Ka ...
2007 Volume 76 Issue 9 Pages
094709
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Dielectric polarization parallel to the [110] direction of a single crystal of the triangular lattice antiferromagnet CuFeO
2 has been measured by a pyroelectric method in pulsed high magnetic fields up to 43 T applied along the [001] direction. No distinct spontaneous dielectric polarization
P is detected in the fourth field-induced phase with a noncollinear spin structure and 4-, 5-, and 3-sublattice phases with commensurate collinear spin structures. Among five magnetic phases that appear in magnetic fields, a finite
P is observed only in the first field-induced phase with the incommensurate noncollinear spin structure. We also confirmed that
P in the first field-induced phase is predominantly oriented within the (001) plane. A strong history dependence has been observed in
P, and is interpreted in terms of the alignment and repopulation of magnetic
Q-domains. The experimental technique for measuring
P in pulsed high magnetic fields is described in detail.
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Kiyokazu Myojin, Ryusuke Ikeda
2007 Volume 76 Issue 9 Pages
094710
Published: September 15, 2007
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Field-tuned superconductor–insulator transition (FSIT) behavior in two-dimensional (2D) isotropic and homogeneous thin films is usually accompanied by a nonvanishing critical resistance at low
T. It is shown that, in a 2D film including line defects paralle to each other but with random positions perpendicular to them, the (apparent) critical resistance in low
T limit vanishes, as in the one-dimensional (1D) quantum superconducting (SC) transition, under a current parallel to the line defects. This 1D-like critical resistive behavior is more clearly seen in systems with weaker point disorder and may be useful in clarifying whether the true origin of FSIT behavior in the parent superconductor is the glass fluctuation or the quantum SC fluctuation. As a by-product of the present calculation, it is also pointed out that, in 2D films with line-like defects with a long but
finite correlation length parallel to the lines, a quantum metallic behavior intervening the insulating and SC ones appears in the resistivity curves.
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Akira Iyo, Yasumoto Tanaka, Hijiri Kito, Yasuharu Kodama, Parasharam M ...
2007 Volume 76 Issue 9 Pages
094711
Published: September 15, 2007
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We have proposed a
Tc vs
n relationship for multilayered high-
Tc superconductors from the analysis of HgBa
2Ca
n−1Cu
nO
y grain-aligned samples containing
n=6 to 16 phases. The sample showed a large and sharp superconducting transition at 105 K in its susceptibility vs temperature curve. This means that multilayered HgBa
2Ca
n−1Cu
nO
y can maintain a high
Tc at least up to
n≈16, otherwise many transitions would have been observed. It is generally believed that the highest
Tc decreases with
n for
n≥4–5 for multilayered superconductors. We conclude that the highest
Tc is almost constant above about
n=5 if the factors reducing
Tc, such as disorder, are eliminated for multilayered superconductors. This behavior can be explained using an inhomogeneous charge distribution model in multilayered cuprates.
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Kensuke Inaba, Akihisa Koga
2007 Volume 76 Issue 9 Pages
094712
Published: September 15, 2007
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We investigate the infinite-dimensional two-orbital Hubbard model at arbitrary band fillings. By means of the self-energy functional approach, we discuss the stability of the metallic state in the systems with same and different bandwidths. It is found that the Mott insulating phases are realized at commensurate band fillings. Furthermore, it is clarified that the orbital selective Mott phase with one orbital localized and the other itinerant is stabilized even at fractional band fillings in the system with different bandwidths.
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Tetsuya Fukushima, Kazunori Sato, Hiroshi Katayama-Yoshida, Peter H. D ...
2007 Volume 76 Issue 9 Pages
094713
Published: September 15, 2007
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We have investigated the electronic structure and magnetism of Mn-doped half-Heusler alloys by using the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) method within the local density approximation (LDA). Half-Heusler compounds can be attractive for spintronic applications because the crystal structure and lattice constant of these compounds are similar to those of III–V and II–VI compounds, which are often used in present semiconductor technologies. The Curie temperatures of Mn-doped half-Heusler alloys are calculated by the mean field approximation, random phase approximation, and Monte Carlo simulation. Based on our calculation results, we discuss whether or not the half-Heusler-based dilute magnetic semiconductors are useful for realizing semiconductor spintronics.
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Xu Yanbing, Ding Huajie, Zhang Shengdong, Yuan Shuanggui, Yang Weifan, ...
2007 Volume 76 Issue 9 Pages
095001
Published: September 15, 2007
Released on J-STAGE: August 12, 2010
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Jun Ohkubo
2007 Volume 76 Issue 9 Pages
095002
Published: September 15, 2007
Released on J-STAGE: August 12, 2010
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Kenji Goto, Masashi Fujisawa, Hidekazu Tanaka, Yoshiya Uwatoko, Akira ...
2007 Volume 76 Issue 9 Pages
098001
Published: September 15, 2007
Released on J-STAGE: August 12, 2010
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Kenji Goto, Toyotaka Osakabe, Kazuhisa Kakurai, Yoshiya Uwatoko, Akira ...
2007 Volume 76 Issue 9 Pages
098002
Published: September 15, 2007
Released on J-STAGE: August 12, 2010
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