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Masato Asai, Kazuaki Tsukada, Shin–ichi Ichikawa, Akihiko Osa, Y ...
Subject area: Nuclear decay and radioactivity.
1996 Volume 65 Issue 5 Pages
1135-1138
Published: May 01, 1996
Released on J-STAGE: October 01, 1999
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A new neutron-rich isotope
166Tb produced in 16 MeV proton-inducedfission of
238U has been identified using the JAERI on-lineisotope separator (JAERI-ISOL) coupled to a gas-jet transport system.Dy KX-rays and γ rays originating from the decay of
166Tb werefound in both mass-166 and 182 fractions, where the
166Tb nuclides were mass-separated as elemental ions
166Tb
+ and monoxide ions
166TbO
+, respectively.The half-life of
166Tb has been determined as 21±6 s, which is much shorter than theoretical predictions.A decay scheme of
166Tb has been proposed and a probable spinassignment for the
166Tb ground state has been discussed.
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Hiroki Saito, Hiroyuki Hyuga
Subject area: Optics.
1996 Volume 65 Issue 5 Pages
1139-1142
Published: May 01, 1996
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Field evolution in a cavity including a time-varying dielectric is studied by determining the effective Hamiltonian. For a uniform dielectric, the Hamiltonian is obtained explicitly, and we use it to discuss photon creation in the case of an oscillating dielectric constant. It is shown that the mode amplification is similar to that in the case of a moving mirror, but the intermode transition is suppressed. This property enables us to amplify a selected mode alone, unlike in the moving mirror case.
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Fuyuki Shimojo, Kozo Hoshino, Hideo Okazaki
Subject area: Structure of liquids and solids; crystallography.
1996 Volume 65 Issue 5 Pages
1143-1145
Published: May 01, 1996
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Stable positions of a proton in the protonic conductor Sc-doped SrTiO
3are obtained by a steepest-descents optimization of the ionic configurationsin the first-principles pseudopotential calculation.It is shown that, in a stable ionic configuration, a Ti (or Sc) ion moves away from the proton, while two O ions move towards the proton, from their positions in the ionic configuration of a perfect crystal SrTiO
3, and that an O-H bond is formed, the length of which is about 1.03 Å.The proton is located on the side opposite the Ti(Sc) ion with respect to a line connecting the two O ions, and the H-O-O angle is approximately 13°.
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Kazuhiro Sano
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 5 Pages
1146-1149
Published: May 01, 1996
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We investigate a t-J ladder model by using the numerical diagonalization method. By calculating correlation functions and assuming the Luttinger liquid relation, we obtained a possible phase diagram of the ground state as a function of J/t and electron density n. We also found that behavior of correlation functions seems to be consistent with the prediction based on the Luttinger liquid relation. The result suggests that the superconducting phase appears in the region of J/t >~ 0.5 for high electron density and J/t >~ 2.0 for low electron density.
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Takayuki Uozumi, Kozo Okada, Akio Kotani, Yasuhisa Tezuka, Shik Shin
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 5 Pages
1150-1153
Published: May 01, 1996
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We have measured experimentally and analyzed theoretically the Ti 2p X-ray photoemission spectra (XPS) and the resonant enhancement of valence photoemissionat the Ti 2p threshold for Ti
2O
3.A satellite structure of the 2p XPS isinterpreted as the charge transfer (CT) satellitebased on the analysis with a cluster model.The behavior of the resonant photoemission is understood in terms of the effect of strong covalency hybridization.It is shown that Ti
2O
3 is classified asan intermediate-type insulatorbetween the CT insulator and the Mott-Hubbard insulator.
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Takeshi Sakai, Tomoko Kagayama, Gendo Oomi, Kenji Sumiyama, Yoshiya Ho ...
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 5 Pages
1154-1157
Published: May 01, 1996
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The electrical resistivity, ρ, of amorphous Ce
58Ru
42 alloy (a-CeRu) has been measured as a function of temperature (T) at various pressures (P) up to 14, GPa. At room temperature ρ decreases rapidly with increasing pressure: ∂ log ρ /∂ P=-0.9, GPa
-1 below 2, GPa. The log T dependence in the ρ (T) curve due to Kondo scattering is observed up to 14, GPa. The slope of the ρ vs log T curve decreases with increasing pressure. At 4.2, K the magnetoresistance, {Δ}ρ /ρ, is positive and decreases with increasing pressure. These results suggest that the Kondo temperature, T
K, decreases with pressure in a-CeRu, i.e., the Kondo effect is suppressed by applying pressure.
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Yoshihiko Inada, Hisashi Azuma, Rikio Settai, Dai Aoki, Yoshichika Onu ...
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 5 Pages
1158-1161
Published: May 01, 1996
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We have measured the magnetoresistance of the orthorhombic CeNiSn at high fields up to 15 T and at low temperatures down to 0.4 K. The positive magnetoresistance is found to become dominant with the decrease of temperature for the magnetic field H applied along the b- and c-axes in the transverse configuration between the current J and the field H (J⊥ H). On the other hand, the longitudinal magnetoresistance (J// H) is small in magnitude for H// b and c. For H// a, the magnetoresistance is negative for any current direction. These experimental results have been discussed on the basis of the cyclotron motion of the compensated carriers with closed Fermi surfaces and the reduction of the anisotropic hybridization gap.
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Akira Shimizu
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 5 Pages
1162-1165
Published: May 01, 1996
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The conductance of one-dimensional interacting electron systemsis calculated in a manner similar to Landauer's argument for non-interacting systems. Unlike in previous studies in whichthe Kubo formula was used, the conductance is directly evaluated asthe ratio of current J to the chemical potential difference{Δ} μ between right-going and left-going particles.It is shown that both J and {Δ} μ are renormalizedby electron-electron (e-e) interactions, but their ratio, the conductance, is not renormalized at allif the e-e interactions are the only scattering mechanism.It is also shown that nonequilibrium current fluctuationat low frequency is absent in such a case.These conclusions are drawn for both Fermi liquids (in which quasi-particles are accompanied with the backflow)and Tomonaga-Luttinger liquids.
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Nobuhiro Sue, Yuhei Natsume
Subject area: Superconductivity.
1996 Volume 65 Issue 5 Pages
1166-1169
Published: May 01, 1996
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We investigate the role of the competition between two kinds of wavevectors {Q}_j in the appearance of an anisotropic superconducting gap in 2-dimensional systems on a square lattice with strong antiferromagnetic correlations. We take into account the effect of interaction between carriers via wavevectors, {Q}_1=(± \frac{π}{a}, ± \frac{π}{a}) and {Q}
2x=(± \frac{π}{a}, 0), {Q}
2y=(0, ± \frac{π}{a}). (Here, a is the lattice constant.) We treat the strong coupling superconductivity by using Eliashberg-Migdal equations for superconducting phases. On the basis of the numerical calculation, we discuss how the symmetric properties of the gap and values of T
c are related to the ratio of the strength of interactions for {Q}_1 and {Q}_2.
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Ryusuke Ikeda
Subject area: Superconductivity.
1996 Volume 65 Issue 5 Pages
1170-1173
Published: May 01, 1996
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A nearly perfect vortex lattice in a type II superconductor is expected to be pinned on a macroscopic scale by a small number of pinning sites. To understand this interplay between the periodicity accompanying solidification of vortices and vortex pinnings, the static vortex-glass susceptibility is examined within the lowest Landau level. It is found that, as soon as vortices start to solidify in an extremely clean system (but with point-like pinnings), a vortex-glass instability occurs at least at the mean field level. Based upon this result, the experimental observation in clean YBCO samples that, as point-like pinnings are added in a clean system, the linear dissipations disappear at a lower temperature than the solidification temperature at the same field in clean limit is reasonably explained without invoking the absence of a true vortex-glass transition.
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Nobuo Furukawa
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1174-1177
Published: May 01, 1996
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As an effective model to describe the perovskite-type manganates (La, A)MnO_3, the double-exchange model (the Kondo lattice modelwith ferromagnetic couplings) on a cubic lattice is investigated. The spin excitation spectrum of the model in theground state is studied using the spin wave approximation.The spin wave dispersion relation observed in the inelasticneutron scattering experiment for La
0.7Pb
0.3MnO
3 is reproduced. Effective values for the electron bandwidth as well as Hund's coupling are estimated from the data.
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Masahiko Isobe, Yutaka Ueda
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1178-1181
Published: May 01, 1996
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Stoichiometric powder samples of α '-NaV
2O
5 were synthesized and the magnetic susceptibility was measured in the temperature range from 2, K to 700, K. The magnetic susceptibility has a good fit to the equation for an S=1/2 antiferromagnetic Heisenberg linear chain with J/k
B=280, K and g=2 above 34, K. Below 34, K the magnetic susceptibility rapidly decreases with decreasing temperature to a constant value of 1.49× 10
-4, emu/V
4+-mol which is reasonable for spin-singlet V
4+--V
4+ pairs. This rapid reduction of the spin susceptibility below 34, K suggests the existence of a spin-Peierls transition. α '-NaV
2O
5 is a possible spin-Peierls compound with the highest critical temperature yet observed.
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Hidetoshi Fukuyama, Tetsuhiro Tanimoto, Masako Saito
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1182-1185
Published: May 01, 1996
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A theoretical possibility of the existence of disorder-induced antiferromagnetic long range order in spin-Peierls system has been presented, which will be in accordance with the recent experimental indication of the coexistence of dimerization and antiferromagnetism in CuGe
1-ySi_yO
3.
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Naoya Takeda, Masayasu Ishikawa, Toshiro Takabatake, Toru Shigeoka
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1186-1188
Published: May 01, 1996
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Low-temperature physical properties of a polycrystal and a single crystal of CePt
2Sn
2 are discussed. The low-temperature specific heat, C(T), and the ac magnetic susceptibility, χ
ac(T), were measured for both samples down to temperatures of 0.15, K and 0.03, K, respectively. The polycrystalline sample showed an antiferromagnetic transition at T
N=0.8, K. The single crystal did not exhibit a long-range magnetic transition at 0.8, K, but exhibited a very sharp cusp in χ
ac(T) at 0.38, K and a broad peak in C(T) at around 0.45, K. These anomalies in the case of the single crystal are attributed to a spin-glass transition at T
sg=0.38, K. The results for the polycrystal and the single crystal suggest that the previously proposed very-heavy-Fermion state is not realized in CePt
2Sn
2 but the enhanced C(T)/T is largely attributable to magnetic phase transitons of the localized moments of Ce
3+.
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Nagahide Izumi
Subject area: Dielectric properties and materials.
1996 Volume 65 Issue 5 Pages
1189-1190
Published: May 01, 1996
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Single-crystal N(CH
3)
4N(C
2H
5)
4CoBr
4 was grown from an aqueous solution by a slow evaporation method, and dielectric properties were measured over the temperature range from -190°C to 50°C. Four phases, phase I (T>-164°C), phase II (-164°C>T>-172°C), phase III (-172°C>T>-179°C) and phase IV (-179°C>T) were recognized and we found that phase II and phase III are ferroelectric and antiferroelectric phases, respectively.
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Kenichi Asano, Tsuneya Ando
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 5 Pages
1191-1194
Published: May 01, 1996
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The effects of electron-electron interactions on two-component cyclotron resonance are studied numerically in a two-dimensional system. The resonance can be considered roughly as consisting of two peaks if a broadening introduced phenomenologically is sufficiently large. At low temperatures the two peaks repel each other and their intensities are modified strongly, while they merge into a single peak at high temperatures. The results qualitatively explain recent experiments on spin-split cyclotron resonance in GaAs/AlGaAs heterostructures.
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Tamao Matsumoto, Ken–ichi Kan’no, Minoru Itoh, Nobuhito Oh ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 5 Pages
1195-1198
Published: May 01, 1996
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Auger-decay-free core luminescence in RbF, CsF, CsCl, CsBr and BaF
2 has been studied under monochromatic vacuum ultraviolet light excitation using a time-resolved technique. Luminescence spectra associated with core holes are carefully separated from those originating in the valence-band excitation. Based on the spectral shape and energy range of the luminescence bands, a lattice relaxation effect following the core hole creation is discussed.
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Yasunori Yamazaki, Shiro Ninomiya, Fumihiro Koike, Hideki Masuda, Tosh ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 5 Pages
1199-1202
Published: May 01, 1996
Released on J-STAGE: October 01, 1999
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Ions of 9, keV/u Ne
9+ are impinged upon a microcapillary target along the capillary axis. X-rays emitted from the projectile downstream of the target show that a part of ions are in multiply excited states keeping a K-shell orbital open, i.e., hollow atoms (ions) are extracted in vacuum. Further, a considerable fraction of them are in extremely stabilized states with lifetimes of -- ns which is more than 10
6 times longer than typical lifetimes of a Ne K-hole. A theoretical prediction suggests that core configurations with high spin multiplicities such as 1s2s2p
4P are potential candidates of the stabilized fraction.
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Hideaki Ujino, Miki Wadati
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 5 Pages
1203-1212
Published: May 01, 1996
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The canonical ensemble is studied for the free quasiparticlesthat describe the thermodynamics of the quantum Calogero model withan arbitrary rational coupling constant.The free quasiparticle is identified with the generalized ideal gaswith mutual statistical interactions.The energy distribution function is numerically computed. Propertiesof the thermal excitation are discussed.
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Kazuhiro Hikami
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 5 Pages
1213-1221
Published: May 01, 1996
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The quantum open Toda lattice is studied by the methodof the separation of variable developed bySklyanin.The quantum canonical operators are derived from the monodromy matrix.Discussed is alsothe relativistic open Toda lattice.
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Johan Springael, Xing–Biao Hu, Ignace Loris
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 5 Pages
1222-1226
Published: May 01, 1996
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We construct an infinite family of soliton equations, the lowest member of which corresponds to the Ito-equation: using the bilinear formalism, we obtain a generic bilinear form leading to a recursion operator for this family. A generic Lax-pair and bilinear Bäcklund-transformation are also reported.
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Shuichi Murakami, Miki Wadati
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 5 Pages
1227-1232
Published: May 01, 1996
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The quantum nonlinear Schrödinger model with two-component fermions exhibits a Yangian symmetry when considered on an infinite interval. We construct the generators of the Yangian using one representationof the degenerate affine Hecke algebra. We discuss the connection between the Yangian symmetry and the quantum inverse scattering method.Under the Yangian algebra the space of states with a fixed particle number forms a tensor product representation of fundamental representations.
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Noriko Akutsu, Yasuhiro Akutsu
Subject area: Statistical physics and thermodynamics.
1996 Volume 65 Issue 5 Pages
1233-1242
Published: May 01, 1996
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For a two-dimensional frustrated Union Jack Ising model, we give exact calculations of anisotropic interface tension, equilibrium crystal shape (ECS), squared scaled interface width and interface entropy by an extended Feynman-Vdovichenko's random walk method.In addition to the region where the reentrant phase transition occurs, we find a wide area of the quasi-reentrant region where an interface entropy is negative and ECS extends with increasing temperature.
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Keiji Saito, Shinji Takesue, Seiji Miyashita
Subject area: Statistical physics and thermodynamics.
1996 Volume 65 Issue 5 Pages
1243-1249
Published: May 01, 1996
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We discuss in detail statistical mechanical properties of quantum dynamics withthe use of numerical simulations of isolated one-dimensional spin systems of various sizes. With respect to the energy distributionin a subsystem, a good agreement is observed between those obtained by the method of statistical mechanics and via long-time average over simulation, even in the system composed of a small number of spins. In particular, the distribution of energy forms the canonical distribution.
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Hikaru Kitamura, Setsuo Ichimaru
Subject area: Nuclear reactions and scattering: general.
1996 Volume 65 Issue 5 Pages
1250-1255
Published: May 01, 1996
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Temporal evolution of enhanced pycnonuclear reactions and resultantthermohydrodynamic expansion in ultrahigh-pressure liquid-metallic hydrogenhave been analyzed by taking into account the heating effect of the chargedfusion yields and the cooling effect by radiation. It is predicted thatthe p-d reactions, starting with the initial conditions for the fuelmaterial, (mass density, temperature, pressure)=(10 g/cm^3, 900 K, 130 Mbar), may last for10
-3 fs, yielding a net gain of thermal energy by a factor of10^4; the temperature 4× 10^5 K, attained in the final stage, may not be high enough to re-ignite thermonuclear reactions, however.The d-t reactions, starting with the initial conditions(10^4 g/cm^3, 16, 100 K, 10^7 Mbar), may last for10
-3 fs and yield a thermal gain by a factor of 24, raising thefuel temperature to approximately 4× 10^7 K, which is sufficientto re-ignite the thermonuclear reactions, leading to a total gain factor of90.
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Naohito Iwasa, Toru Motobayashi, Yoshiaki Ando, Meiko Kurokawa, Hiroyu ...
Subject area: Nuclear reactions and scattering: specific reactions.
1996 Volume 65 Issue 5 Pages
1256-1263
Published: May 01, 1996
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The Coulomb-dissociation cross section for the process ^8B →^7Be + p in the field of
208Pb was measured at E(^8B) = 46.5 A MeV. The
7Be(p, γ)
8B cross section relevant to the high-energy ^8B solar-neutrino productionwas extracted at E
C.M. = 0.6 - 1.7 MeV. Two theoretical models on the structure of ^8B were used to evaluatepossible corrections due to M1 and E2 admixtures to the dominant E1cross sections. Their overall effect is shown to besmall regardless of the choice of the models. The present result is consistent with the results of the direct measurements of Filippone et al. and Vaughn et al. within errors. This result suggests further studies with the Coulomb-dissociation method to extract astrophysical S
17 factor at -- 20 keVrelevant to the high-energy solar-neutrino flux.
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Nobukazu Kondo, Yoshiomi Kondoh
Subject area: Fluid dynamics.
1996 Volume 65 Issue 5 Pages
1264-1269
Published: May 01, 1996
Released on J-STAGE: October 01, 1999
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An attractor of dissipative structures in solitons described by the Korteweg-de Vries (K-dV) equation with a viscous dissipation termis investigated, with the use of an eigenfunction spectrum analysis associated with the dissipative dynamical operator[Phys. Rev. E 49 (1994) 5546]. It is shown numerically and quantitatively that the basic procesess for the self-organization of dissipative soliton are spectrum transfer by nonlinear interaction and selective dissipation among the eigenmodes of the dissipative operator.It is quantitatively shown that an interchange between the dominant operators occurs during nonlinear self-organization processes, which leads to a final self-similar coherent structure uniquely determined by the dissipative operator.
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Retsuo Kawakami, Shinya Okuda, Takahumi Miyazaki, Nobuaki Ikuta
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1996 Volume 65 Issue 5 Pages
1270-1276
Published: May 01, 1996
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In order to understand the variety of ion mobilities in gases under common ion-neutral interaction potentials, systematic calculations have been performed assuming the 12-4 inverse power potentials with several force constants. It is found that the momentum-transfer collision frequencies calculated from the potentials as functions of relative speed can definitively explain the feature of mobilities. As a result, ion mobilities with and without a hump, with positive and negative derivatives referred to reduced electric field and to gas temperature have been clearly understood in relation with the potential shapes.
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Tomejiro Yamagishi, Heiji Sanuki
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1996 Volume 65 Issue 5 Pages
1277-1283
Published: May 01, 1996
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Anomalous cross field plasma fluxes induced by the electric field fluctuations has been evaluated in a rotating plasma with shear flow in a helical system. The anomalous ion flux is evaluated by the contribution from ion curvature drift resonance continuum in the test particle model. The radial electric field induces the Doppler frequency shift which disappears in the frequency integrated anomalous flux. The inhomogeneity of the electric field (shear flow effect), however, induces a new force term in the flux. The curvature drift resonance also induces a new force term ‹ B›
′/‹ B› which, however, did not make large influence in the ion flux in the CHS configuration. The shear flow term in the flux combined with the electric field in neoclassical flux reduces to a first order differential equation which governs the radial profile of the electric field. Numerical results indicate that the shear flow effect is important for the anomalous cross field flux and for determination of the radial electric field particularly in the peripheral region.
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Shinichiro Toda, Sanae –I. Itoh
Subject area: The physics of plasmas and electric discharges.
1996 Volume 65 Issue 5 Pages
1284-1289
Published: May 01, 1996
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An extended model theory for Edge Localized Modes (ELMs) is presented with inclusion of the effects of the radial electric field shear, E
r′, for high temperature plasmas in tokamaks. The dynamic model consists of an electric bifurcation model for the L/H transition, which contains a hysteresis characteristic due to E
r′, and of a dynamic transport equation for the plasma gradient parameter. The self-generated oscillation is found to occur even if the effects of E
r′ are included: in addition to those of the radial electric field.The condition for the occurrence of a self-generated oscillation is examined. The wider region in the parameter space is found for the case with a negative electric field shear than for the case with a positive one.
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Makoto Iwata, Sadamitsu Harada, Yoshihiro Ishibashi
Subject area: Mechanical and acoustical properties of condesed matter.
1996 Volume 65 Issue 5 Pages
1290-1292
Published: May 01, 1996
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Temperature dependence of the elastic stiffness constant in [N(CH
3)
4]
2CoBr
4 single crystal has been measured between room temperature and 288, K by means of the ultrasonic pulse echo overlap method. In the room temperature phase (phase I), softening of the elastic constant c
55 has been observed. The transition temperature has been determined to be T
c=287.6, K.
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Tomoyuki Hikita, Kazuo Itoh, Naoya Okada, Naoki Ohkubo, Etsuko Kodera
Subject area: Equations of state, phase equilibria, and phase transitions.
1996 Volume 65 Issue 5 Pages
1293-1296
Published: May 01, 1996
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The langbeinite-type K
2Fe
2(SO
4)
3 was synthesized. The temperature dependence of the dielectric constant shows a clear anomaly at about 130 K. Mössbauer spectrum of
57Fe was recorded in the temperature range from 15 to 290 K. The spectrum at all temperatures consists of two doublets which are analyzed with isomer shifts and quadrupole couplings. The quadrupole splitting of one site is 3.00 mm/s at 290 K and shows only 10% increase down to 15 K. The other one is 0.82 mm/s at 290 K and shows a drastic increase, resulting at 15 K in 2.5 times that at 290 K. The two
57Fe sites for the electric field gradient were assigned to the two crystallographically inequivalent iron sites compairing the two octahedral oxygen environments of the iron ions. The broad background spectrum is interpreted as the distribution of the electric field gradient due to the multi-positional distribution in SO
4 groups proposed by Itoh {et al.
View full abstract
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Kazuo Gesi
Subject area: Equations of state, phase equilibria, and phase transitions.
1996 Volume 65 Issue 5 Pages
1297-1301
Published: May 01, 1996
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The effect of hydrostatic pressure on the low-temperature structural phase transitions in N(CH
3)
4XBr
3 (X, : Mn, , Ni, , Cd) has been studied. The I--II transition temperatures of N(CH
3)
4MnBr
3 (140, K at atmospheric pressure), N(CH
3)
4NiBr
3 (135, K), and N(CH
3)
4CdBr
3 (161, K; the ferroelectric Curie temperature) increase linearly with increasing pressure with coefficients of 0.075, K/MPa, 0.092, K/MPa, and 0.086, K/MPa, respectively. As pressure increases the II--III transition temperature of N(CH
3)
4NiBr
3 (97, K) decreases with a pressure coefficients of -0.07, K/MPa. The results are compared with those previously reported for N(CH
3)
4XCl
3-type crystals (X, : Mn, , Cd) and discussed.
View full abstract
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Masahiko Higuchi, Akira Hasegawa
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 5 Pages
1302-1311
Published: May 01, 1996
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The Fermi surface is investigated for the heavy-electron compound CeRu
2, which is known as a type-II superconductor exhibiting anomalous magnetic properties, on the basis of the itinerant-electron model for the 4f electrons. The energy band structure is calculated by a relativistic linear augmented-plane-wave method with the exchange-correlation potential in the local-density approximation. The Fermi surface is found to consist of a set of six small hole pockets, a large multiply-connected hole sheet and a set of three complex electron sheets and a set of three small electron pockets. Recent experimental results for the de Haas-van Alphen effect are explained reasonably well in terms of the large hole sheet and the small electron pockets except for the cyclotron effective mass. It seems that many frequency branches may have been missed in the experiment. A nesting property of the Fermi surface is also investigated.
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Teruki Motohashi, Keiso Hayashi, Masanori Matoba, Shuichiro Anzai, Ats ...
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 5 Pages
1312-1316
Published: May 01, 1996
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In order to study the change of the electronic states from the charge-transfer(CT) type metal to the Mott-Hubbard(MH) one, X-ray photoemission spectra are measured on the NiAs-type (Co
1-xV_x)
0.91S (x ≤ 0.50) and V
0.91S. The asymmetry parameter α for S 2s and 2p core level spectra decrease with increasing x. This result indicates that the local density of states of S atoms at the Fermi level decreases as x increases; the system changes from the CT-type metal to the MH-one with x.The change in V 2p line shape with x suggests the possibility of the considerable hybridization between V 3d and S 3p in (Co
1-xV_x)
0.91S at lower x region. This feature would be related to the appearance of the extra peak at binding energy E
B = 2--3, eV in the valence band X-ray photoemission spectra.
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Yoshitaka Arikabe, Makoto Kuwabara, Yoshiyuki Ono
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 5 Pages
1317-1324
Published: May 01, 1996
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The dynamical behavior of an acoustic polaron in typical non-degenerate conjugated polymer, polydiacetylene, is numerically studied by using Su-Schrieffer-Heeger's model for the one dimensional electron-lattice system. It is confirmed that the velocity of a polaron accelerated by a constant electric field shows a saturation to a velocity close to the sound velocity of the system, and that the width of a moving polaron decreases as a monotonic function of the velocity tending to zero at the saturation velocity. The effective mass of a polaron is estimated to be about one hundred times as heavy as the bare electron mass. Furthermore the linear mode analysis in the presence of a polaron is carried out, leading to the conclusion that there is only one localized mode, i.e. the translational mode. This is confirmed also from the phase shift of extended modes. There is no localized mode corresponding to the amplitude mode in the case of the soliton in polyacetylene. Nevertheless the width of a moving polaron shows small oscillations in time. This is found to be related to the lowest odd symmetry extended mode and to be due to the finite size effect.
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D. D. Sarma
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 5 Pages
1325-1328
Published: May 01, 1996
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With extensive calculations based on cluster and impurity models, we analyse core level photoemission spectra of several transition metal compounds. Our results show that the average d-occupancy is determined with sufficient accuracy from these spectra, though different interaction strengths, like U, {Δ} and t individually have a very wide range of uncertainties. It is also found that an analysis of core level spectra of a stoichiometric compound can provide a good estimate even for the character of doped holes in such systems.
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Hideyuki Sato, Hitoshi Sugawara, Yuji Aoki, Kazuyuki Motoki, Rikio Set ...
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 5 Pages
1329-1333
Published: May 01, 1996
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We have measured the Hall effect, magnetoresistance, thermoelectric power, magnetic susceptibility and magnetization in CeAg and LaAg single crystals. We observed clear anomalies related with a ferromagnetic transition at 5.5, K and a quadrupolar ordering at 17, K both in the Hall effect and magnetic susceptibility for CeAg.
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Kentaro Kyuno, Jae–Geun Ha, Ryoichi Yamamoto, Setsuro Asano
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1996 Volume 65 Issue 5 Pages
1334-1339
Published: May 01, 1996
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The anisotropy energies of (111) and (001) oriented Ag/Fe and Au/Fe multilayers are obtained by a first-principle calculation to investigate the orientational dependence of the magnetic anisotropy. All systems show perpendicular anisotropy in good agreement with experiments. In the case of Ag/Fe multilayers, the anisotorpy energy of the (001) oriented multilayer is larger than that of the (111) multilayer. In contrast to Ag/Fe, Au/Fe(111) multilayer exhibits a stronger perpendicular anisotropy than the (001) oriented system. In all systems, a large minority-spin LDOS of |m| =2 character of Fe near the Fermi energy could be the origin of perpendicular magnetic anisotropy.
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Tokutaro Komatsu, Nozomu Matsukawa, Takeharu Inoue, Gunzi Saito
Subject area: Superconductivity.
1996 Volume 65 Issue 5 Pages
1340-1354
Published: May 01, 1996
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The resistivity, thermoelectric power (TEP), ESR and static susceptibility were measured on κ - and κ '-(BEDT-TTF)
2Cu
2(CN)
3; also, a band calculation based on an extended Hückel method was re-examined and the results were compared with those of related BEDT-TTF (ET) salts. Although the crystal- and calculated band structures of these salts are identical within experimental error, the former is a semiconductor; on the contrary, the latter is a metal at ambient pressure (AP). The band calculation and the spin susceptibility (χ
spin) measurement suggest that the former salt is a Mott-insulator with an exactly half-filled band. Although κ -(ET)
2Cu
2(CN)
3 shows only the ESR signal of ET cation radicals, the κ '-salt shows an additional ESR signal of Cu
2+ below about 20, K. The content of Cu
2+ is 88--1200, ppm of total copper atoms. It is found that the metallic state and the superconductivity at AP of κ '-(ET)
2Cu
2(CN)
3 is realized by a band-filling control by substituting Cu
+ with Cu
2+.
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Takafumi Kita
Subject area: Superconductivity.
1996 Volume 65 Issue 5 Pages
1355-1372
Published: May 01, 1996
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A theory of a Fermi superfluid is formulated based on the condensate wave function of the configuration space.First, two basic ingredients areextracted from the wave function, i.e. the effective condensate wave function v(x
1, x
2) and the quasiparticle field γ (x) with xdenoting the space and spin coordinates r{α}.After transforming a Hamiltonian into a normal-ordered productof γ, a perturbation expansionwith respect to the quasiparticle interaction is formulatedfor both the thermodynamic potential {Ω}and the one-particle density matrix ρ.The thermodynamic potential thus obtained includes the normal-state expression of Luttinger and Ward as the limit of v→ 0.The density matrix is written as a sum of the coherent part ρ
(c)and the quasiparticle part ρ
(q), where ρ
(c) is expressed only with respect to v(x
1, x
2).It is shown that v and γ are responsible forthe coherent and thermodynamic properties respectively.Thus the present formalism gives a microscopic foundation for the two-fluid model.Connections with the Gor'kov equations and the Bogoliubov-de Gennes equations are also clarified.It is found that the one-particle density matrices of those formalismsare not equivalent to ρ of the present formalism.The origin of the angular momentum paradox of
3He, -Ais traced to this difference.
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Takafumi Kita
Subject area: Superconductivity.
1996 Volume 65 Issue 5 Pages
1373-1382
Published: May 01, 1996
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The formalism of the preceding paper is applied to a system of uniform flow.Explicit expres\-sions are obtained for the specific heat: C
V, the superfluid-density tensor: ρ, and the spin susceptibility of the singlet pairing: χ.It is the quasiparticle excitation near the excitation thresholdthat is responsible for these quantities.The three expressions for v→0 reduce to the normal-state results of Luttinger;the Leggett expressions of ρ and χare reproduced by neglecting the feedback effects.
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Yasuharu Koyata, Hideki Nakamura, Nobuyuki Iwata, Akihiro Inomata, Kay ...
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1383-1386
Published: May 01, 1996
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We made measurements of dielectric constant, pyroelectric current, magnetic susceptibility and magnetoelectric effect of single crystals of YbMn
2O
5. From the results, we concluded that there were two phase transitions besides antiferromagnetic transition at approximately 40, K.The first transition at 32, K is characterized by a peak of dielectric constant, a kink of magnetoelectric polarization and an appearance of pyroelectricity below this temperature. It was considered to be electric in nature. The second one is at 6, K. It is also accompanied by another peak of dielectric constant, a steep rise of pyroelectricity and anomalies of both magnetic and magnetoelectric susceptibilities. We suppose that the ordering of Yb
3+ magnetic moments begins to develop at this temperature, involving a change in the crystal structure and then in spontaneous polarization. The low temperature phase has a magnetic field-induced transition which occurs at about 19, kOe at 4.2, K.
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Hidetsugu Kitatani, Takehiko Oguchi
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1387-1391
Published: May 01, 1996
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A new type of argument for the existence of an exact dimer ground state in a class of S=1/2 quantum Heisenberg spin systems is presented which gives a necessary and sufficient conditions for the existence of an exact dimer ground state in contrast to the previous arguments which give only the sufficient conditions.
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Masashi Hase, Kunimitsu Uchinokura, Robert J. Birgeneau, Kazuma Hirota ...
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1392-1398
Published: May 01, 1996
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A recent study of the magnetic susceptibility in single crystals of the spin-Peierls material CuGeO
3 doped with Zn indicates antiferromagnetic order at low temperatures. In the present publication, we report a neutron scattering investigation of the static and dynamic magnetic properties of single-crystal Cu
0.966Zn
0.034GeO
3. Below the transition temperature of 4.2 ± 0.3 K, sharp magnetic Bragg peaks are observed at the magnetic superlattice positions (0 k l/2) with both k and l odd. However, the intensities of these peaks are not saturated even at 1.4 K, and the long range ordered magnetic moment is only -- 0.2 μ
B per Cu site. Moreover, no well-defined spin-wave-like excitations are seen. Instead, overdamped magnetic excitations appear around the magnetic Bragg peaks at low temperatures. These results suggest an unusual state of magnetic order incorporating considerable magnetic and possibly structural disorder. We speculate that this unusual order is caused by a spatial distribution of spin states due to local spin-Peierls distortions.
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Kohei Murao, Fumitaka Matsubara, Tsutomu Kudo
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1399-1403
Published: May 01, 1996
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We study the magnetic ordering of an anisotropic Heisenberg ferromagnet on a triangular lattice with antiferromagnetic next-nearest-neighbor interactions by means of the mean field theory and a computer simulation. We find that, as the temperature is decreased, an incommensurate short-range order state and a ferromagnetic long-range phase appear successively. The phase transition between them is of the first order and the relaxation time of the transition is very long. Hence, we suggest that the low temperature phase realized in nature is a domain state in which ferromagnetic domains with various sizes are tangled with each other. We also suggest that the model would be applicable to the compound LiNiO_2.
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Tetsuya Takeuchi, Parhat Ahmet, Melike Abliz, Rikio Settai, Yoshichika ...
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1404-1408
Published: May 01, 1996
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The Jahn-Teller effect and metamagnetic transition in single crystalline PrCu
2 have been studied by thermal expansion and magnetostriction measurements in the paramagnetic state. The linear thermal expansion in the temperature range from 1.8 to 300, K is found to be quite anisotropic in the whole temperature range, which is due to the highly anisotropic crystalline electric field. The magnetostrictions along the three crystallographic axes in the field along the c-axis also indicate anisotropic behavior with an extremely large length change and large hysteresis. It is clarified that the metamagnetic transition with the conversion of the Ising axis in PrCu
2 is due to the large modification of the crystalline electric field by the field-induced structural phase transition.
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Ayumu Kida, Masaaki Matsui
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1409-1412
Published: May 01, 1996
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Multilayers of [7ML Fe/14ML Cu] on Cu(001) were prepared. A rearrangement of Fe atoms is observed, when Fe is deposited on a flat Cu-buffer surface. The degree of rearrangement depends on the flatness of the buffer surface. The structure of the rearrangement is 3D-(n × 1), n = 2, 3, 4, 5 etc. and the mean magnetic moment of the Fe atoms in a sample which contains many rearranged atoms is about 0.7 μ
B, while that of a sample mainly with fcc structure is 1.6 μ
B. The various values of Fe moments for multilayers with the same design are corresponding to the mixture of the 3D-(n × 1) and fcc structures in the film. The fcc structure of Fe is obtained when Fe is deposited on a rough Cu-buffer surface.
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Kiyosi Terao
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1413-1417
Published: May 01, 1996
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By making use of the Luttinger-Tisza method on the classical Heisenberg model, we examine how the isochoric distortions affect the frustrated spin system in YMn
2 with the cubic Laves phase structure. The distance dependece of the exchange parameter is taken into account by perturbational calculation. It is shown that the spin system orders in layered configurations or the YMn
2 type configuration under the influence of tetragonal distortion.
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Tatsuo Fukuda, Yasuo Endoh, Kazuyoshi Yamada, Masayasu Takeda, Shinich ...
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 5 Pages
1418-1426
Published: May 01, 1996
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Inelastic neutron scattering experiments were carried out on the spin density wave (SDW) state of a single-Q chromium crystal. We made systematic investigations in a wide energy range up to ω -- 100 meV by combining the triple axis and time-of-flight neutron spectroscopy. The q profile of the inelastic scattering is of a three-peaked structure; the commensurate scattering (CMS) at the antiferromagnetic superlattice and the incommensurate scattering (ICMS) near the wave vector points of the static SDW. In the longitudinal SDW state the dynamical susceptibility for the CMS increases with increasing ω and eventually overwhelms that for the ICMS. The ICMS, on the other hand, reaches a maximum at ω -- 20 meV. This cross-over phenomenon is reflected in the temperature dependence of the magnetic excitations so that the CMS dominates at temperatures above 200 K.
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