巻号一覧
69 巻, 4 号
選択された号の論文の43件中1～43を表示しています
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Xianguo Geng, Wen–Xiu Ma2000 年 69 巻 4 号 p. 985-986
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありAn isospectral problem with multipotentials and the corresponding hierarchy of nonlinear evolution equations are proposed, in which a typical system is the coupled nonlinear diffusion equations.抄録全体を表示PDF形式でダウンロード (75K) -
Naoki Kawashima2000 年 69 巻 4 号 p. 987-990
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe two-dimensional Edwards-Anderson model with Gaussian bond distribution is investigated at T=0 through a numerical method. Droplet excitations are directly observed. It turns out that the averaged volume of droplets is proportional to lD with D = 1.80(2) where l is the spanning length of droplets, revealing their fractal nature. The exponent characterizing the l dependence of the droplet excitation energy is estimated as θD' = -0.42(4), clearly different from the stiffness exponent for domain wall excitations.抄録全体を表示PDF形式でダウンロード (133K) -
Takashi Odagaki, Osamu Yamamuro, Mariko Higuchi, Takasuke Matsuo2000 年 69 巻 4 号 p. 991-992
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe report evidence that for a class of fragile-glass formers, the excess specific heat in the supercooled state near the glass transition temperature can be scaled by a parameter defined as the product of temperature and configurational entropy. We also show that the scaling does not hold for some alcohols and thus it can be used to classify the glass formers.抄録全体を表示PDF形式でダウンロード (100K) -
Wilson Agerico Diñ o, Hideaki Kasai, Ayao Okiji2000 年 69 巻 4 号 p. 993-996
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe report on how we can influence the dynamics of H2 dissociation by changing the orientation dependence of the reaction. To demonstrate, we examined H2 dissociation across the Cu-Pt bridge site of an ordered Cu3Pt(111). Our density-functional-theory-based potential energy surface calculation results reveal a considerable activation barrier, with an orientation dependence that exhibits preference for H2 orientations parallel to the surface over all other orientations, and preference for H2 orientations perpendicular to the surface over orientations intermediate between perpendicular and parallel. Our calculated dissociation probability results reveal nonmonotonic dependence on the initial rotational state of the impinging H2, and we suggest how further information regarding the orientation dependence of the reaction could be determined experimentally.抄録全体を表示PDF形式でダウンロード (205K) -
Mitake Miyazaki, Keita Kishigi, Yasumasa Hasegawa2000 年 69 巻 4 号 p. 997-999
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe have investigated the effect of uniaxial pressure on the transition temperature of spin-density-wave (SDW) in quasi-one-dimensional organic conductors. Although the imperfectness of the Fermi surface nesting is reduced when the hopping matrix element ta increases by uniaxial pressure along the most conducting a axis, which is favorable for the SDW state, the decrease of density of the state due to the increase of ta suppresses the SDW transition. As a result, TSDW decreases as ta increases. This is consistent with the recent experimental result for (TMTSF)2PF6 under uniaxial strain along the a axis.抄録全体を表示PDF形式でダウンロード (127K) -
Kazuhiro Sano2000 年 69 巻 4 号 p. 1000-1003
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe study the Luttinger-liquid parameter Kρ of the Hubbard chain and the Hubbard ladder models using the ordinary perturbation method combined with the Luttinger-liquid relation. According to the Luttinger-liquid relation, the critical exponent Kρ is related to the charge susceptibility χc and the Drude weight D by K sb ρ =½(π χc D)1/2. By calculating these quantities with the perturbation method, we obtain Kρ on the first-order analytically and up to the second-order numerically. We compare these results with the results of the Bethe ansatz for the Hubbard chain and those of the numerical diagonalization for the Hubbard ladder. This comparision shows that the perturbation calculation of Kρ is reliable in the weak coupling regime.抄録全体を表示PDF形式でダウンロード (172K) -
Hiroko Matsuda, Keizo Endo, Kiyoshi Ooiwa, Masanori Iijima, Yoshihiko ...2000 年 69 巻 4 号 p. 1004-1007
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありElectrical resistivity (ρ), magnetoresistance (MR) and magnetization (σ) for Heusler type alloys Fe2+xV1-xAl with -0.10≤ x≤ 0.20 were measured. A giant magnetoresistance (GMR) of about 40% was observed for the weakly inhomogeneous ferromagnet Fe2.1V0.9Al at 4.2 K in 130 kOe. In the ferromagnetic alloys (x≥ 0.10) the ρ showed a maximum near the Curie temperature (TC) and the temperature coefficient of resistivity (TCR) was negative above TC. For the paramagnetic alloys (x≤ 0.05) TCR was negative in the entire temperature (T) range examined. In the low T range, the alloys with x≤ 0.10 exhibited variable-range hopping (VRH) conduction behavior, ln ρ ∝ T-1/4. The magnetism of the present alloys was explained on the basis of the concept of magnetic clusters. The origin of the present GMR was discussed in relation to the Anderson localization of carriers in alloys having atomic and magnetic disorders.抄録全体を表示PDF形式でダウンロード (168K) -
Keiichi Katoh, Yuko Hosokoshi, Katsuya Inoue, Tsuneaki Goto2000 年 69 巻 4 号 p. 1008-1011
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe have synthesized the novel organic polyradicals BIP-BNO and BIP-TENO, which crystallize to form spin systems with a double spin chain, where BIP-BNO and BIP-TENO denote 3, 5'-bis(N-tert-butylaminoxyl)-3', 5-dibromobiphenyl and 3, 3', 5, 5'-tetrakis(N-tert-butylaminoxyl)biphenyl, respectively. The crystals of BIP-BNO form a two-leg ladder of S=1/2 with antiferromagnetic legs and rungs. The ground state of this material is singlet. The BIP-TENO molecule includes S=1/2 spin pairs (dimers) in which the two spins are coupled ferromagnetically. The BIP-TENO crystals form a double spin chain consisting of dimers. All dimers interact antiferromagnetically with each other. This system can be regarded as an antiferromagnetic two-leg ladder when the dimer is taken as a unit. The ground state of this material is singlet and the existence of excitation gaps is suggested by the temperature dependence of the static magnetic susceptibility.抄録全体を表示PDF形式でダウンロード (194K) -
Takashi Nishioka, Yoshikazu Tabata, Toshifumi Taniguchi, Yoshihito Miy ...2000 年 69 巻 4 号 p. 1012-1015
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありA new intermetallic compound Ce2AgIn3 has been prepared and found to crystallize with the hexagonal CaIn2-type structure. We report the results of ac and dc magnetic susceptibility (χac and χdc), specific heat (C) and electrical resistivity (ρ) measurements on this compound. At around 1.8 K, the real part in χac shows a cusp and the nonlinear part in χdc diverges, while there are no anomalies in both C and ρ. On the other hand, ρ increases slightly with decreasing temperature below 10 K and C/T at 0.5 K is large at 780 mJ/K2mol-Ce. These results indicate that Ce2AgIn3 is a spin glass of good quality and also belongs to the heavy fermion system.抄録全体を表示PDF形式でダウンロード (149K) -
Kenzo Onizuka, Hiroshi Kageyama, Yasuo Narumi, Koichi Kindo, Yutaka Ue ...2000 年 69 巻 4 号 p. 1016-1018
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありHigh-field magnetization measurements up to 57 T have been performed at 0.08 K in a single crystal of a two-dimensional spin-gap material SrCu2(BO3)2. We successfully observed the predicted plateau at 1/3 of the total magnetization around 50 T, in which the magnetic superstructure is characterized by a novel stripe order of triplets. The 1/3 plateau is much wider than the previously observed 1/4 and 1/8 plateaux.抄録全体を表示PDF形式でダウンロード (132K) -
Chiaki Uyeda, Kouichi Ohtawa, Kazuyuki Okita2000 年 69 巻 4 号 p. 1019-1022
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありSmall diamagnetic anisotropy, (Δ χ)DIA, on the order of 10-9 to 10-10 emu/g was detected for four silicates by the use of the field-induced harmonic-oscillation method in the high-temperature region. The measured Δ χ-T relations were effective to separate the Δ χ component caused by the paramagnetic impurity ions. The obtained maximum (Δ χ)DIA values between two magnetic principal axes are (2.1±0.1)×10-9 emu/g [b-a axes] for orthoclase, (3.5±0.1)×10-9 emu/g [b-a axes] for petalite, (0.8±0.1)×10-9 emu/g [a-c axes] for scapolite and (3.8±0.1)×10-9 emu/g [a-c axes] for apophyllite. The (Si, Al)O4 tetrahedral frameworks composing the crystal structures of the silicates are considered to be the origin of the observed (Δ χ)DIA values.抄録全体を表示PDF形式でダウンロード (148K) -
Masahiro Matsumura, Tomohiko Ikeda, Hideki Yamagata2000 年 69 巻 4 号 p. 1023-1026
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありCu-NQR spectra were measured in the wide temperature range of 300 K to 1.5 K to examine the possibility of the occurrence of the static spin-charge stripe order in La2-xBaxCuO4 with x=1/8. The usual NQR spectrum is observed above Td2, the structural transition temperature from the LTO to LTT phase. Below Td2, the signal intensity decreases rapidly with decreasing temperature, which is accompanied with the abrupt increase of the effective spin echo decay rate, while no significant changes appear in its lineshape down to 10 K. Below 10 K, the spectrum starts to spread and exhibits unusual broadening with a tail to about 80 MHz at 1.5 K. The abnormally broad spectrum at 1.5 K, which is regarded as evidence of the static spin and/or charge order, is simulated satisfactorily in terms of the stripe order proposed for La2-x-yNdySrxCuO4 (x=1/8) with the assumption of the modulation amplitude for Cu moment of about 0.24 μB.抄録全体を表示PDF形式でダウンロード (173K) -
Emmanuel Yomba, Timoléon Crépin Kofané2000 年 69 巻 4 号 p. 1027-1032
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありAnalytical solutions of a lowest order complex Ginzburg-Landau (LOCGL) equation ψt + V ψx = χ ψ + p ψxx - q0| ψ|2 ψ-q1|ψ|2 ψx - q2|ψ|x2 ψ - q3ψ2 bar ψ x - q4|ψ|4ψ are examined, using a method derived from the Painlevé test for integrability and Hirota's bilinear formalism. In particular, we have introduced the Puiseux expansion in order to take into account the quintic nonlinear term in the previous model. Solitary wave, periodic unbounded wave and shock-type wave are obtained as exact solutions of the above mentioned equation.抄録全体を表示 -
Tetsu Yajima2000 年 69 巻 4 号 p. 1033-1041
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありGeneric forms of the initial conditions for a soliton equation in the Ablowitz-Kaup-Newell-Segur (AKNS) hierarchy which can be solved in terms of the hypergeometric function are presented. A detailed study on these conditions shows that the initial wave packets are generally consisted of only one pulse, and not symmetric around their peaks. The scattering problems associated with the initial conditions are also studied. The presented initial conditions yield a set of complete scattering data and expressions of soliton solutions explicitly.抄録全体を表示 -
Xing–Biao Hu, Zuo–Nong Zhu, Dao–Liu Wang2000 年 69 巻 4 号 p. 1042-1049
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありA differential-difference Caudrey-Dodd-Gibbon-Kotera-Sawada equation is proposed. The corresponding Bäcklund transformation is presented. A Lax pair for it is found. A nonlinear superposition formula is also derived based on the permutability of the Bäcklund transformation.抄録全体を表示 -
Hiroshi Sato, Kazuo Sasaki2000 年 69 巻 4 号 p. 1050-1054
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe phase transition of the two-dimensional, three-state chiral clock model is studied by using the density matrix renormalization group method and the finite-size renormalization group technique. The transition temperature and the critical exponent ν of the correlation length are calculated for the transition from the commensurate to paramagnetic phases. It is found that ν is anisotropic and that ν for the correlation along the chiral axis decreases with increasing the chiral field Δ while the one perpendicular to the axis increases with Δ.抄録全体を表示 -
Tomohiro Sasamoto2000 年 69 巻 4 号 p. 1055-1067
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe one-dimensional partially asymmetric simple exclusion process with open boundaries is considered. The stationary state, which is known to be constructed in a matrix product form, is studied by applying the theory of q-orthogonal polynomials. Using a formula of the q-Hermite polynomials, the average density profile is computed in the thermodynamic limit. The phase diagram for the correlation length, which was conjectured in ref.~ citen me99 [J. Phys. A 32 (1999) 7109], is confirmed.抄録全体を表示 -
Nabil N. Abd–Allah2000 年 69 巻 4 号 p. 1068-1074
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありNuclear emulsions are used to investigate spallations produced by 4.5 A GeV/c 24Mg and 28Si nuclei. The integral multiplicity distribution of disintegrated particles from target nuclei is used to separate the inelastic interactions with the free hydrogen (H), the light (CNO), and the heavy (AgBr) nuclei. Angle of flow, transverse momentum, angular characteristics, and azimuthal alignment data are analyzed for the presence collective fragments in 24Mg+Ag(Br) and 28Si+Ag(Br) collisions with emulsion nuclei at 4.5 A GeV/c. The determination of the reaction plane is powerful tool for investigating the nucleus-nucleus interactions. The analysis of the projection of the transverse momentum, angular characteristics, azimuthal alignment and range onto the reaction plane shows a significant side splash of the target fragment.抄録全体を表示 -
Reima Iwatsu, Tetuya Kawamura2000 年 69 巻 4 号 p. 1075-1083
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありNumerical method is developed which is capable of computing the buoyancy driven flows within an enclosure with large temperature differences. Numerical procedure is constructed on the system of truncated equations which is derived from the assumption that the flow Mach number is small. Numerical results are compared with available bench mark solutions for natural convection within a square enclosure and it is found that the outcome is highly satisfactory. Based on the confirmation of the accuracy and efficiency of the present methodology, exemplary computations are performed on the natural convection flows within enclosures with various complex configuration, in order to exhibit the applicability of the present computational method. Present numerical method will be extended to include turbulence modeling in the future studies toward the practical goal of simulating the flows associated with room fire.抄録全体を表示 -
Yosuke Yoshimura2000 年 69 巻 4 号 p. 1084-1092
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありIndirect interaction between hard spheres through solvent molecules is studied in a square-well fluid by a Monte Carlo method. The solvophobic interaction between hard spheres induced by the solvent-solvent interaction is repulsive in a close distance and attractive in the outer region. The solvophobic interaction extends to long distance at a medium density about half of the density of the usual liquid, while it has a local characteristic at the high density. The solvophobic interaction relies on the competition in the decrease of both the repulsive and the attractive indirect forces with the increase in the solvent-solvent interaction. The complicated fluid structure between the hard spheres is responsible for the larger decreasing rate of the repulsive force, which leads to the molecular association by the solvophobic interaction.抄録全体を表示 -
Takashi Onozuka, Komajiro Niizeki2000 年 69 巻 4 号 p. 1093-1099
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありVariation of the lattice-modulation period pa of the `incommensurate' phase Bi2Sr2(Ca1-xPrx)Cu2O8+δ (0≤ x≤ 0.72) with Pr-concentration x was examined by electron diffraction, and the domain configuration by high-resolution transmission electron microscopy (HRTEM). The plot of pa versus x exhibits roughly a linear decrease but it has a staircase structure. The period of each stair, pa, agrees with a value expected for a commensurate structure. We observed nine stairs which are symmetrically arranged; the central stair corresponds to the primary structure with a simple modulation, and a stair on the left (or right) is associated with an advanced (or delayed) discommensuration. On the other hand, the number of domain configurations i.e. commensurate structures observed by HRTEM is seventeen. The observed staircase structure covers a full range of commensurate structures predicted theoretically. The pattern observed in the plot of pa versus x is consistent with the simulation based on the Frenkel-Kontrova model and an inhomogeneity hypothesis.抄録全体を表示 -
Hideya Onodera, Kentaro Indoh, Hisao Kobayashi, Satoru Kunii, Yasuo Ya ...2000 年 69 巻 4 号 p. 1100-1104
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe have measured the 161Dy Mössbauer effects on the cubic ferroquadrupolar ordering compound DyB6. In the antiferromagnetic phase, the Mössbauer spectra are interpreted well by a single set of hyperfine parameters which gives the Dy magnetic moment of 9.8 μ B. The nuclear quadrupole splitting implies that the crystal field parameter A20 originating from the rhombohedral strain by the ferroquadrupoler ordering is positive. Based on these facts, we conclude that the antiferromagnetic structure is a collinear one where the Dy moment direction is nearly parallel to the strain axis (the cubic [1~1~1] axis). Reflecting the 4f electronic state that two or more Kramers doublets are quasi-degenerated, the spectra in the ferroquadrupolar ordered and paramagnetic phases can not be analyzed well by the two-level relaxation model.抄録全体を表示 -
Yoshihumi Tokiwa, Hisatomo Harima, Dai Aoki, Sayaka Nojiri, Masao Mura ...2000 年 69 巻 4 号 p. 1105-1112
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe succeeded in growing a single crystal of USi3 with the cubic crystal structure and measured the transverse magnetoresistance and de Haas-van Alphen(dHvA) oscillation. Fifteen dHvA branches were observed, ranging from 7.37×106 to 2.33×108 Oe. These branches are in good agreement with theoretical ones based on 5f-itinerant FLAPW band calculations. Cyclotron masses, which are in the range from 0.39 to 4.17 m0, are approximately the same as the corresponding band masses. These results indicate that the itinerant 5f-electrons form wide bands. The magnetoresistance results confirmed the existence of open orbits, which can be well explained by the band 10-electron Fermi surface.抄録全体を表示 -
Masakazu Murakami2000 年 69 巻 4 号 p. 1113-1124
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありPossible ordered states in the 2D extended Hubbard model with on-site (U>0) and nearest-neighbor (V) interaction are examined near half filling, with emphasis on the effect of finite V. First, the phase diagram at absolute zero is determined in the mean field approximation. For V<0, a state where dx2-y2-wave superconductivity (dSC), commensurate spin-density-wave (SDW) and π-triplet pair coexist is seen to be stabilized. Here, the importance of π-triplet pair on the coexistence of dSC and SDW is indicated. This coexistent state is hampered by the phase separation (PS), which is generally expected to occur in the presence of finite-range attractive interaction, but survives. For V>0, a state where commensurate charge-density-wave (CDW), SDW and ferromagnetism (FM) coexist is seen to be stabilized. Here, the importance of FM on the coexistence of CDW and SDW is indicated. Next, in order to examine the effects of fluctuation on each mean field ordered state, the renormalization group method for the special case that the Fermi level lies just on the saddle points, (π, 0) and (0, π), is applied. The crucial difference from the mean field result is that superconductivity can arise even for U>0 and V≥q0, where the superconducting gap symmetry is dx2-y2-wave for U>4V and s-wave for U<4V. Finally, the possibilities that the mean field coexistent states survive in the presence of fluctuation are discussed.抄録全体を表示 -
Yasuhiro Asano, Taichiro Kato2000 年 69 巻 4 号 p. 1125-1135
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe discuss the magnetoconductance oscillations in small junctions of a ballistic semiconductor and a superconductor. The conductance is calculated both numerically and analytically based on the Bogoliubov-de Gennes equation. The conductance oscillations appear when the Andreev reflection is not perfect at the interface and the diameter of the cyclotron motion of a quasiparticle is comparable to the width of the junction. An interplay between the cyclotron motion of a quasiparticle near the interface and the phase shift by the magnetic field is the origin of the conductance oscillations.抄録全体を表示 -
Hirohiko Sato, Odd E. Andersson, Toshiaki Enoki, Itsuko S. Suzuki, Mas ...2000 年 69 巻 4 号 p. 1136-1144
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありIn order to consider the dimensionality and the interaction between conduction electrons and localized magnetic moments, angular dependences of the magnetoresistance of magnetic GIC's, stage-1 and stage-2 MCl2 GIC's (M=Cu and Co) were measured. The c-axis (perpendicular to the graphite layers) resistance of stage-1 CuCl2 GIC shows a typical angular dependent magnetoresistance oscillation (ADMRO) which is commonly observed in several quasi two-dimensional (2D) electron systems with a periodically-warped cylindrical Fermi surface. This proves a band conduction along the c-axis in spite of extremely large anisotropy in conductivity (ρc/ρa = 105). On the other hand, stage-2 CoCl2 GIC shows a larger MR for the magnetic field along the c axis than that along the graphitic plane. In addition, ADMRO is absent in this compound. These suggest that the c-axis conduction is governed by incoherent interlayer hoppings. The angular dependence of MR in stage-2 CuCl2 and stage-1 CoCl2 GIC's show an intermediate behavior between that of stage-1 CuCl2 GIC and stage-2 CoCl2 GIC. The above material-dependence is attributed to the difference in interlayer coupling and suggests a dimensional crossover from a highly anisotropic three-dimensional (3D) system (stage-1 CuCl2 GIC) to an almost pure 2D system (stage-2 CoCl2 GIC). The c-axis resistances of stage-1 and stage-2 CoCl2 GIC's reflect also the magnetic states of Co spins. This phenomenon is explained in terms of a model based on spin-dependent tunneling effect.抄録全体を表示 -
Shinji Nonoyama, Akira Oguri2000 年 69 巻 4 号 p. 1145-1151
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe spatial distribution of the nonequilibrium current and charge distributions in a series of two point contacts are studied in the presence of a magnetic field making use of a recursive Green function method based on the Keldysh formalism. Numerical results show that the structure of vortices appearing in between two barriers depends strongly on the applied bias voltage. The chemical potential dependence of the total current is also investigated.抄録全体を表示 -
Yukio Tanaka, Satoshi Kashiwaya2000 年 69 巻 4 号 p. 1152-1161
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありProperties of the DC Josephson effects in unconventional-superconductors under the presence of an exchange field in the insulator are studied theoretically. The current-phase relation of the DC Josephson current I( varphi) and the temperature dependence of the maximum Josephson current IC(T) are calculated for various pairing symmetries and crystal orientations as a function of the exchange interaction strength (Im). The influences of the spin-orbit coupling are also discussed. The phase dependent energy levels of quasiparticle bound states are sensitive to the magnitude of Im, orientaions of the junctions, and especially parities of two supercondctors. When the two superconductors have d-wave symmetries, IC(T) shows non-monotonous behavior on the magnitude of Im, and accordingly the Josephson junction changes between “0-junction” and “π-junction”. On the other hand, when the two superconductors have different parities, e.g. s-wave and p-wave, the Josephson current is largely suppressed due to SU(2) symmetry in the spin space in the absence of Im. However, the Josephson current rapidly recovers with the increase of Im because of the breakdown in SU(2) symmetry. These anomalous features can be used as a criteria for the identification of the pairing symmetries in novel superconductors.抄録全体を表示 -
Toshiyuki Ozawa, Yoshiyuki Ono2000 年 69 巻 4 号 p. 1162-1169
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe dynamical properties of an acoustic bipolaron in non-degenerate conjugated polymers such as polydiacetylene (PDA), which can be regarded as one-dimensional electron-lattice systems, are studied through numerical simulations. In these simulations, use has been made of Su-Schrieffer-Heeger's model extended to involve on-site as well as nearest-neighbor electron-electron Coulomb repulsion terms. The electron-electron interactions are treated within the unrestricted Hartree-Fock approximation. It is confirmed that the velocity of the acoustic bipolaron accelerated by a constant electric field saturates at the sound velocity of the system, and that the width of the bipolaron shrinks to zero as its velocity approaches the saturation velocity (= sound velocity). The effective mass of a bipolaron is estimated to be several hundred times as heavy as the free electron mass, in the case of PDA. These properties are compared with those of a polaron.抄録全体を表示 -
Chul–Ho Lee, Kazuyoshi Yamada, Yasuo Endoh, Gen Shirane, R. J. B ...2000 年 69 巻 4 号 p. 1170-1176
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe energy spectrum of incommensurate spin fluctuations in superconducting Sr-doped La2CuO4 has been studied by inelastic neutron scattering experiments. An energy gap in the spin excitation spectrum is observed in the superconducting state of optimally doped (x=0.15) and slightly overdoped (x=0.18) samples. At temperatures well below Tc, the incommensurate peaks diminish rapidly in intensity with decreasing energy below --8 meV and merge into the background below --3.5 meV for x=0.15 and --4.5 meV for x=0.18. For both samples, the energy spectrum of the q-integrated spin susceptibility, χ′ ′(ω), exhibits an enhancement around 7 meV, which is caused by a broadening in the momentum width of the incommensurate peaks. The gap-like structure in the energy spectrum and the enhancement of χ′ ′(ω) survive at Tc. On the other hand, for both underdoped (x=0.10) and heavily overdoped (x=0.25) samples there is neither a clear energy gap nor an enhancement of χ′ ′ (ω) below Tc.抄録全体を表示 -
Naoki Kikugawa, Jun’ya Hori, Fumihiko Nakamura, Toshizo Fujita2000 年 69 巻 4 号 p. 1177-1180
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe have investigated the impurity scattering effect due to a small amount of oxygen deficiency on the anisotropic resistivity of La2-xSrxCuO4-δ with δ ≤ 0.01 for x=0.10, 0.15, 0.22 and 0.26. For x where bulk superconductivity is observed at low temperatures, we found that the c-axis conductivity is remarkably enhanced by scattering above the superconducting transition temperature Tc in spite of the negligible effect on Tc and the in-plane conductivity. This enhancement suggests that the conduction along the c axis is nonmetallic and is assisted by the scattering of the carriers confined in the CuO2 plane. The degree of enhancement decreases with increasing x. Finally, the enhancement becomes unclear for x=0.26, where the bulk superconductivity vanishes and the conduction becomes fully metallic along any directions. This is consistent with the idea that the two-dimensionality of the normal electronic state plays an important role in the occurrence of superconductivity at low temperatures.抄録全体を表示 -
Ryotaro Arita, Kazuhiko Kuroki, Hideo Aoki2000 年 69 巻 4 号 p. 1181-1191
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe have systematically studied superconducting instabilities in the repulsive Hubbard model for d-wave and p-wave pairing in various 2D and 3D lattices. Using fluctuation exchange approximation, we consider 3D face centered cubic lattice, 3D body centered cubic lattice, 3D simple cubic lattice, 2D square lattice and 2D triangular lattice, where either strong ferro- or antiferromagnetic spin fluctuations are present. We show that (i) d-wave instability mediated by antiferromagnetic spin fluctuations is stronger than p-wave instability mediated by ferromagnetic spin fluctuations both in 2D and 3D, and (ii) d-wave instability in 2D is much stronger than that in 3D. These amount that the “best” situation is the antiferromagnetic-fluctuation mediated in 2D as far as the single-band Hubbard model on ordinary lattices are concerned.抄録全体を表示 -
Tatsuo Komori, Hajime Yoshino, Hajime Takayama2000 年 69 巻 4 号 p. 1192-1201
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありUsing Monte Carlo simulations, we have studied isothermal aging of three-dimensional Ising spin-glass model focusing on quasi-equilibrium behavior of the spin auto-correlation function. Weak violation of the time translational invariance in the quasi-equilibrium regime is analyzed in terms of effective stiffness for droplet excitations in the presence of domain walls. Within the range of computational time window, we have confirmed that the effective stiffness follows the expected scaling behavior with respect to the characteristic length scales associated with droplet excitations and domain walls, whose growth law has been extracted from our simulated data. Implication of the results are discussed in relation to experimental works on ac susceptibilities.抄録全体を表示 -
Osamu Koseki, Fumitaka Matsubara2000 年 69 巻 4 号 p. 1202-1206
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe make a realistic Monte Carlo simulation of the magnetic phase transition of quasi-one dimensional hexagonal antiferromagnets CsCoBr3 and CsCoCl3 using a cluster heat bath method. Results reproduce experimental observations of anomalous behaviors of magnetic quantities around two temperatures TN1 and TN2 ( < TN1). In particular, the rapid increases of the magnetic structure factors F(1/3, 1/3, 1) and F(1, 1, 1) around TN2 without any anomaly of the specific heat are demonstrated. In addition, the mysterious increase of F(1, 1, 1) just below TN1 is reproduced. We suggest that the long-range order phase appearing below TN1 is a single phase described by three sublattices, and the change in the magnetic structure around TN2 is a crossover between a partially disordered antiferromagnet-like phase at higher temperatures and a ferrimagnet-like phase at lower temperatures.抄録全体を表示 -
Toshiya Hikihara, Takashi Tonegawa, Makoto Kaburagi, Tomotoshi Nishino ...2000 年 69 巻 4 号 p. 1207-1218
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe investigate the ground-state phase diagram of the quantum mixed spin chain in which two hbox S=½ and two hbox S=1 spins are arranged alternatively and isotropic exchange interactions between nearest-neighboring pairs of spins are assumed. Guided by our previous results [J. Phys. Soc. Jpn. 67 (1998) 1000] for a few limiting cases of the exchange interactions, we carry out a density-matrix renormalization-group calculation to determine the ground-state phase diagram in detail. From the gapless points of the singlet-triplet energy gap, five boundary lines are determined, which divide the phase diagram into six regions. In three regions the ground states with the Haldane-phase character appear, while in the remaining three regions those with the dimer character appear. We also present a characterization of the phases concerning how the ground state in each phase is represented in the framework of the valence-bond-solid (VBS) picture. Making use of the matrix-product wave function, we classify the VBS pictures and interpret the ground-state phase diagram in terms of symmetries schematically related to the VBS pictures. We investigate the ground-state nearest-neighboring two-spin correlation functions and a kind of string order parameters, by which we confirm the validity of the characterization.抄録全体を表示 -
Jun–ichi Igarashi, Tatsuya Nagao2000 年 69 巻 4 号 p. 1219-1225
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありWe propose an approximate version of the three-body scattering theory as an extension of local approximation. We solve the three-body problem by limiting the number of three-body states, instead of solving the Faddeev equation, in the calculation of the self-energy. Applying this simple extension to the antiferromagnetic state at half-filling in the two-dimensional Hubbard model, we demonstrate that it gives a reasonable spectral function for the single-particle Green's function in comparison with the results of the exact diagonalization for finite clusters and the quantum Monte Carlo method. We also show that it gives the ground state energy and the sublattice magnetization comparable to previous variational Monte Carlo results.抄録全体を表示 -
Takayuki Uozumi, Tetsuo Okane, Kenji Yoshii, Teikichi A. Sasaki, Akio ...2000 年 69 巻 4 号 p. 1226-1233
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありThe observed 3d X-ray photoemission spectra (XPS), resonant 3dXPS (RXPS) at the L3 edge and resonant L3M45M45 Auger electron spectra (RAES) of 4d transition metal oxide PdO are successfully analyzed by means of an impurity Anderson model. The importance of Pd 4d- O 2p hybridization effect is especially emphasized in the interpretation of observed spectra. It causes charge transfer satellites in 3dXPS and L3M45M45RAES and mainly determines the structure of resonance enhancements in 3dRXPS. From the analysis of spectra, 4d-2p charge transfer energy Δ, 4d correlation energy Udd and 4d-2p transfer integral pdσ are estimated to be 5.5 eV, 4.5 eV and 2.1 eV, respectively. The character of the insulating energy gap of PdO is also theoretically investigated: PdO is classified as an intermediate-type insulator due to the strong 4d-2p hybridization.抄録全体を表示 -
Satoshi Kawaguchi, Masayasu Mimura, Tomoyuki Ohya, Hirotaka Okabe, Sho ...2000 年 69 巻 4 号 p. 1234-1244
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証ありIn the germination of seeds, there often observes cluster-formation of well-grown roots and the edge effect phenomenon. During germination and growth before starting photosynthesis, direct interaction such as competition for nutrition among hosts is rather weak because of self-supplying of nutrition. Instead, hormones play an important role and may cause the above experimental observations. In order to understand these aspects, we propose a growth model for root. The hormone effect and its growth-stage-dependent sensitivity are taken into consideration. It is discussed how the growth process of grouping roots is influenced by exogenous hormones secreted from roots.抄録全体を表示 -
Akira Nakamura2000 年 69 巻 4 号 p. 1245-1246
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証あり -
Kimichika Fukushima2000 年 69 巻 4 号 p. 1247-1248
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証あり -
Tadahiko Chida, Shugo Suzuki, Kenji Nakao2000 年 69 巻 4 号 p. 1249-1250
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証あり -
Ken–ichi Matsuda, Satoshi Tanda, Masato Shiobara, Yoshitoshi Oka ...2000 年 69 巻 4 号 p. 1251-1252
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証あり -
Yoshimasa Isawa, Hideto Horii2000 年 69 巻 4 号 p. 1253-1254
発行日: 2000/04/01
公開日: 2000/07/28
ジャーナル 認証あり
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