Showing papers in "Journal of the Physical Society of Japan in 1990"
TL;DR: In this paper, a model for high T c superconductors was proposed by using the self-consistent renormalization theory and the electrical resistivity and the nuclear spin relaxation rate due to the spin fluctuations in the normal state were calculated.
Abstract: Spin fluctuations in antiferromagnetic and nearly antiferromagnetic two dimensional (square lattice) itinerant electron systems, as a possible model for high T c superconductors, are investigated by using the self-consistent renormalization theory. The electrical resistivity and the nuclear spin relaxation rate due to the spin fluctuations in the normal state are calculated. The results in the nearly antiferromagnetic regime as applied to high T c oxides seem to explain the experimental results both in their temperature dependence and in their orders of magnitudes. By using the same spin fluctuations we discuss superconductivity due to the spin fluctuation mechanism within a weak coupling theory. The order parameter is shown to have B 1 g or A 2 g symmetry and the critical temperature is evaluated to be of the right order of magnitude.
450 citations
TL;DR: In this paper, a cellular automaton (CA) of filter automata type is proposed and it is shown that the solitary waves interact with one another preserving their identities during a time evolution.
Abstract: A cellular automaton (CA) of filter automata type is proposed. Any state of the CA consists only of solitary wave solutions. It is shown that the solitary waves interact with one another preserving their identities during a time evolution. It is also shown that the CA has infinitely many conserved quantities. Hence, this CA may be considered to be one of the simplest soliton systems.
381 citations
TL;DR: In this article, a new slab model was proposed for the electronic structure calculation of a polar GaAs(001) surface, which contains fractionally charged H atoms which completely terminate a noninteresting surface of the slab.
Abstract: A new slab model approach is examined for the electronic structure calculation of a polar semiconductor surface. Our proposed slab model contains fractionally charged H atoms which completely terminate a noninteresting surface of the slab. We have studied in detail the electronic structure of the polar GaAs(001) surface in order to examine the reliability of our slab model. Calculation is performed by the ab initio pseudopotential method. We have found that our slab model can accurately describe a polar semiconductor surface. In addition, this model can greatly reduce the computational time.
320 citations
TL;DR: In this article, multilayers consisting of two magnetic components with different anisotropies were prepared by successively depositing Co, Cu, Ni 80 Fe 20 and Cu layers.
Abstract: Multilayers consisting of two magnetic components with different anisotropies were prepared by successively depositing Co, Cu, Ni 80 Fe 20 and Cu layers. By applying a moderate field, the two magnetizations are oriented antiparallel with each other, and then the electric resistance significantly increases due to spin-dependent electron scattering. A large magnetoresistance change, 9.9% at 300 K, was observed in [Co(30 A)/Cu(50 A)/NiFe(30 A)/Cu(50 A)]×15.
242 citations
TL;DR: In this paper, the authors examined relative stability and physical properties of several possible magnetic states in the mean field theory for an itinerant electron model, i.e., the Hubbard model on a two-dimensional square lattice.
Abstract: Spatially modulated magnetic phases are investigated within the mean field theory for an itinerant electron model, i.e. the Hubbard model on a two-dimensional square lattice. By numerically diagonalizing the Hamiltonian for finite-size systems under a periodic boundary condition, we examine relative stability and physical properties of several possible magnetic states. When the electron fillings are nearly half-full, the diagonally or vertically modulated spin density wave (SDW) state is stabilized over the uniform antiferromagnetic state and a crossover from the vertical to the diagonal states appears. The diagonal or vertical stripe state is characterized by the presence of the midgap band due to the soliton lattice formation inside the main SDW gap, being an insulator. The wave length λ SDW is linearly proportional to the excess carrier concentration. Excess carriers are accommodated in the form of the soliton lattice, forming a charge density wave whose wave length is λ SDW /2.
194 citations
TL;DR: In this article, the series of Yb pnictides with anti-Th 3 P 4 structure was investigated, and the valence of the Yb varies from about 2.25 to 2.2 K with the decreasing weight of the Pnictogen and the 4 f level is located around the band gap and the charge ordering below about 300 K.
Abstract: We have investigated the series of Yb pnictides with anti-Th 3 P 4 structure. The valence of Yb varies from about 2 of Yb 4 Bi 3 to 2.25 of Yb 4 As 3 with the decreasing weight of the pnictogen. In the case of Yb 4 As 3 , the 4 f level is located around the band gap and the charge ordering below about 300 K has been observed. Further, in such a situation, we have observed a clear dense Kondo or heavy Fermion behavior in the resistivity, the magnetic susceptibility and the specific heat though the carrier concentration at 4.2 K is only about 0.001/Yb 3+ ion. Yb 4 As 3 is a new heavy Fermion compound which inquires whether the heavy Fermion state needs free carriers.
139 citations
TL;DR: In an attempt to understand angular-dependent oscillatory magnetoresistance phenomena recently discovered in organic conductors, calculations of magnetoreduction in quasi-two-dimensional systems were carried out in the framework of the Boltzmann transport theory as mentioned in this paper.
Abstract: In an attempt to understand angular-dependent oscillatory magnetoresistance phenomena recently discovered in organic conductors, calculations of magnetoresistance in quasi-two-dimensional systems were carried out in the framework of the Boltzmann transport theory. Calculated magnetoresistance curves show the angular-dependent oscillations reminiscent of those found experimentally. It is argued that the essential physics underlying the resistance oscillations lies in the angular dependence of the high field asymptotic behavior (saturation vs divergence) of semiclassical magnetoresistance which arises from Fermi surface topology.
133 citations
TL;DR: In this article, the ground state of double quantum well systems was investigated theoretically and numerically in the strong magnetic field limit, and it was shown that when the separation between the electron layer and the hole layer, d, is small, an excitonic condensate state is realized.
Abstract: Two-dimensional electron-hole systems with long excitonic life-times can be realized in double quantum well systems by applying an electric field which localizes electrons and holes in opposite wells. The ground state of such a system is investigated theoretically and numerically in the strong magnetic field limit. It is shown that when the separation between the electron layer and the hole layer, d , is small, an excitonic condensate state is realized. On the other hand, when d is large, either independent fractional quantum Hall states for electrons and holes or coupled Wigner crystal (dipole density wave) states may be realized depending on the filling factor. The difference in photoluminescence spectra between these states is discussed.
131 citations
TL;DR: In this paper, the real time dynamics of a moving charged soliton in polyacetylene is studied numerically by using Su-Schrieffer-Heeger's model, where an electric field is introduced to the system through a time dependent vector potential which can be included into the Hamiltonian through the Peierls substitution of the phase factor to the transfer integral.
Abstract: Real time dynamics of a moving charged soliton in polyacetylene is studied numerically by using Su-Schrieffer-Heeger's model. An electric field is introduced to the system through a time dependent vector potential which can be included into the Hamiltonian through the Peierls substitution of the phase factor to the transfer integral. Several interesting properties of the moving soliton are obtained, e.g. , the Brownian-like motion of the soliton due to the soliton-phonon interaction, the saturation of the soliton velocity, the saturation velocity being independent of the applied electric field strength, while the time needed to attain the saturation velocity is, roughly speaking, linearly dependent on the logarithm of the applied field.
126 citations
TL;DR: In this paper, a variational wave function is introduced to describe the Hubbard model in strong correlation in the presence of Intersite correlation (or Jastrow) factors beyond the Gutzwiller wave function.
Abstract: New variational wave functions are introduced to describe the Hubbard model in strong correlation Intersite correlation (or Jastrow) factors are taken into account beyond the Gutzwiller wave function (GF) A study is made on the one-dimensional lattice and the two-dimensional square lattice at half-filling as well as less-than-half-filling Much improvement can be achieved thereby in the description of physical quantities such as the momentum distribution and spin and charge density correlation functions In addition, the ground state energy is lowered appreciably compared with the GF In this connection, the Mott-Hubbard-type metal-insulator transition is also re-examined
124 citations
TL;DR: In this article, a new approach to the study of one dimensional quantum spin systems at finite temperature is presented, based upon a general structure of solvable models; the Yang-Baxter equation and the Bethe ansatz equation, and in addition the evaluation of finite size corrections.
Abstract: Presented is a new approach to the study of one dimensional quantum spin systems at finite temperature. The approach is based upon a general structure of solvable models; the Yang-Baxter equation and the Bethe ansatz equation, and in addition the evaluation of finite size corrections. Provided that the ground state is constructed by the Bethe ansatz method, exact low temperature expansions of physical quantities are given without further assumption.
TL;DR: In this article, the temperature dependence of both the Knight shift tensor and the nuclear spin-lattice relaxation rate (1/T 1 ) in the normal state have been studied, by using the magnetically oriented powered samples of YBa 2 Cu 3 O 6+ x with x = 0.96, 0.8 and 0.6.
Abstract: The temperature dependence of both the Knight shift ( K ) tensor and the nuclear spin-lattice relaxation rate (1/ T 1 ) in the normal state have been studied, by using the magnetically oriented powered samples of YBa 2 Cu 3 O 6+ x with x =0.96, 0.8 and 0.6. From the K -χ plot for the planer oxygen sites (O(2, 3)), we have determined the principal values of the hyperfine field tensor and found that those hardly depend on the hole concentration. The remarkable feature has emerged from the T -dependence of the 1/( T 1 T ) at the O(2, 3) sites; i.e. it reveals almost the same T -dependence of the spin parts of the Knight shift. This observation suggests that the energy width of the spin excitations around q ∼0 is T -independent in the normal state. The Knight shift tensor at the apical oxygen sites has also been measured and is discussed.
TL;DR: In this paper, the magnetic properties of four intermetallic compounds, e, e 1, κ and η, in manganese-germanium system are studied by means of magnetization measurement and neutron diffraction.
Abstract: Magnetic properties of four intermetallic compounds, e, e 1 , κ and η, in manganese-germanium system are studied by means of magnetization measurement and neutron diffraction. Exchange coefficients of the interaction between Mn atoms in the compounds are estimated quantitatively using the molecular field approximation, based on the localized moment model. The exchange coefficient between Mn atoms on different sublattices is found to depend largely on the interatomic distance: The exchange coefficient is found to be negative for smaller interatomic distances than r c =2.9 A and positive for larger distances. The magnitude of atomic magnetic moment in the compounds is consistently discussed using the Pauling valence, after Mori and Mitsui (J. Phys. Soc. Jpn. 25 (1968) 82).
TL;DR: In this article, the structure analysis of K 3 H(SO 4 ) 2 was performed by X-ray diffraction experiments in order to study the hydrogen bond character in connection with the geometrical isotope effect.
Abstract: Structure analysis of K 3 H(SO 4 ) 2 was performed by X-ray diffraction experiments in order to study the hydrogen bond character in connection with the geometrical isotope effect. Crystal data at room temperature were obtained as a=9.777(1)A, b=5.674(1)A, c=14.667(4)A, β=102.97(2)° and the space group A 2/ a , Z =4. The hydrogen bond length R OO determined from the positional parameters was 2.493(1)A which was close to but still longer than the so called critical bond length r c . The electron density of split hydrogen atoms was observed on a differential Fourier map. It is concluded that the hydrogen atoms take the disordered state at room temperature and the distance between hydrogen atoms R HH is approximately 0.65 A. The possibilities for the existence both of the low temperature phase and the high temperature prototype phase are discussed.
TL;DR: In this article, a pure one-dimensional lattice with quartic anharmonicity and nearest-neighbor interactions is shown to exhibit a fairly well-defined propagating self-localized mode above the harmonic frequency band.
Abstract: A pure one-dimensional lattice with quartic anharmonicity and nearest-neighbor interactions is shown to exhibit a fairly well-defined propagating self-localized mode above the harmonic frequency band. This is a propagating-mode version of a stationary, immobile p-like self-localized mode having the displacement pattern (···, 0, 0, -1/2, 1/2, 0, 0, ···) in the extreme localization limit. An approximate analytical expression for localized-mode envelope functions is obtained in a form similar to that of the Ablowitz-Ladik lattice solitons. Nonlinear eigenvalue equations are studied by using the method of lattice Green's functions, by which an approximate analytical expression for the dispersion relation of the localized mode is also obtained.
TL;DR: In this paper, a quantum phenomenology for heavy-fermion systems is formulated, where the effective Lagrangian for low-energy excitations contains a localized spinfluctuation part which is coupled with an itinerant fermion part.
Abstract: A quantum mechanical phenomenology for heavy-fermion systems is formulated. The effective Lagrangian for low-energy excitations contains a localized spin-fluctuation part which is coupled with an itinerant fermion part. Each part represents the dual nature of strongly correlated f electrons. The coupling parameter is fixed by comparison with the Fermi-liquid theory for the Anderson model. The comparison also fixes the localized spin-fluctuation spectrum. As an advantage over the Fermi-liquid description the present model takes into account the RKKY interaction and non-linear effects of spin polarization. A formula for the magnetic equation of state is derived which is applicable to the metamagnetism and weak antiferromagnetism in heavy-fermion systems.
TL;DR: In this paper, the ground state of the CuO 6 octahedron in La 2-x Sr x CuO 4 changes from 1 A 1 g to 3 B 1 g near the observed onset concentration of superconductivity.
Abstract: By the first-principles variational calculations we show that, with the increase of Sr concentration, the ground state of CuO 6 octahedron in La 2- x Sr x CuO 4 changes from 1 A 1 g to 3 B 1 g near the observed onset concentration of superconductivity while the ground state of the CuO 4 cluster in Nd 2- x Ce x CuO 4 is always 3 B 1 g in the presence of dopant electrons. Based on this result, two kinds of phase diagrams are predicted for hole- and electron-doped superconductors. These results support the spin polaron mechanism proposed by Kamimura et al .
TL;DR: In this paper, a new refined model of the L-mode and H-mode transition in tokamaks is presented based on the bifurcation of the radial electric field, E r, near the edge.
Abstract: A new refined model of the L-mode and H-mode transition in tokamaks is presented based on the bifurcation of the radial electric field, E r , near the edge. The radial gradient of E r is newly introduced to explain the sudden change of fluctuations as well as plasma fluxes at the onset of transition. This nodel predicts that the L- to H-mode transition is associated with the decrease of d E r /d r causing reduction of particle and energy fluxes at the critical gradient.
TL;DR: In this article, the early stage of the polarization reversal in the present model coincides with what described by the Kolmogorov-Avrami (KA) model, and the characteristics of the model are discussed in the relationship with the KA model.
Abstract: The ferroelectric switching process has been studied on the basis of a one-dimensional discrete lattice model. The characteristics of the model is discussed in the relationship with the Kolmogorov-Avrami(KA) model. It has turned out that the features in the early stage of the polarization reversal in the present model coincides with what described by the KA model.
TL;DR: In this article, the amplitude of a soliton decreases asymptotically as x − 1/2, where x being the distance of the propagation is the distance from the source to the sink.
Abstract: A partial differential equation which describes nonlinear wave propagations in random media is presented. Based on the equation, behaviors of soliton propagations can be analysed exactly. Under the assumption of Gaussian white randomness, it is shown that the amplitude of a soliton decreases asymptotically as x −1/2, x being the distance of the propagation.
TL;DR: In this article, three-step metamagnetic transitions are obtained with the transition fields of 358, 365 and 396 kOe at 1.3 K. The experimental results are explained quantitatively by introducing the model that the heavy Fermion state produced by the mixing of the f- and conduction electrons is destroyed by applying the field and that the exchange interactions between the recovered local f-electron magnetic moments on the uranium atom play an important role on the magnetic properties at high field.
Abstract: High-field magnetization and magnetoresistance of URu 2 Si 2 single crystal are investigated up to 600 kOe. Three-step metamagnetic transitions are obtained with the transition fields of 358, 365 and 396 kOe at 1.3 K. The experimental results are explained quantitatively by introducing the model that the heavy Fermion state produced by the mixing of the f- and conduction electrons is destroyed by applying the field and that the exchange interactions between the recovered local f-electron magnetic moments on the uranium atom play an important role on the magnetic properties at high field. The frustration due to the exchange interactions induces the three-step metamagnetic transitions.
TL;DR: In this article, the authors analyzed NQR/NMR in high T c oxides and showed quantitatively that 17 (1/T 1 ), 89 (1 /T 1 ) and the approximate T -linear behavior of 63 ( 1 / T 1 ) at higher temperatures can be associated with the same d-spin fluctuations around q ∼ 0.
Abstract: Nuclear relaxation experiments of 63 Cu, 17 O and 89 Y NQR/NMR in high T c oxides have been analyzed within the frame of a phenomenological model proposed by Mila and Rice, supposing that only one spin freedom exists. It was shown quantitatively that 17 (1/ T 1 ), 89 (1/ T 1 ) and the approximate T -linear behavior of 63 (1/ T 1 ) at higher temperatures can be associated with the same d-spin fluctuations around q ∼0. The anisotropy data of 63 (1/ T 1 ) were also explained consistently, from which the values of hyperfine coupling constants were determined. The contribution of antiferromagnetic d-spin fluctuations to 63 (1/ T 1 ) was extracted from raw data without any adjustable parameters . The saturated value of it above ∼150 K is by an order of magnitude lower than that estimated in a localized moment scheme. A possible interplay between magnetism and superconductivity is also discussed.
TL;DR: In this article, a new numerical method is proposed for multidimensional linear advection equations, which uses a cubic spatial profile within grids, and is described in an explicit form by assuming that both a physical quantity and its spatial derivative obey the given equation.
Abstract: A new numerical method is proposed for multidimensional linear advection equations. The scheme uses a cubic spatial profile within grids, and is described in an explicit form by assuming that both a physical quantity and its spatial derivative obey the given equation. The method gives a stable and less diffusive result without any flux limiter. Its extension to nonlinear equations with nonadvection term is straightforward.
TL;DR: In this paper, a gap-type valence fluctuating compound CeNiSn was studied and it was proved that no magnetic ordering occurs down to 0.38 K. This behavior can be well interpreted by a quasiparticle band model which possesses a band width of 140 K and a low energy excitation inside an energy gap of 14 K at the Fermi level.
Abstract: 119 Sn NMR study has been made in a gap-type valence fluctuating compound CeNiSn. From the measurements of Knight shift and the nuclear spin lattice relaxation time T 1 of 119 Sn, it is proved that no magnetic ordering occurs down to 0.38 K. The relaxation rate, 1/ T 1 markedly decreases below 30 K down to 0.40 K. This behavior can be well interpreted by a quasiparticle band model which possesses a band width of 140 K and a low energy excitation inside an energy gap of 14 K at the Fermi level. Then it is clarified from the microscopic point of view that the pseudo-gap formed at the Fermi level has a character that the quasiparticle density of state is linearly proportional to the energy near the Fermi level at low temperatures.
TL;DR: In this paper, the magnetization and thermal expansion measurements have been made on the same samples of Fe x Co 1-x Si alloys and they have been analyzed on the basis of the spin fluctuation theory developed by Takahashi to obtain information on the nature of spin fluctuations of this system.
Abstract: Both magnetization and thermal expansion measurements have been made on the same samples of Fe x Co 1- x Si alloys. The magnetization data is analyzed on the basis of the spin fluctuation theory developed by Takahashi to obtain information on the nature of spin fluctuations of this system. We found that concentration variation of magnetic behaviors of the ferromagnetic alloys, such as the Arrott plots and the temperature dependence of spontaneous magnetization, is quantitatively well explained by the theory. Magnetovolume coupling constant is also estimated from thermal expansion coefficient on the basis of the SCR theory over the wide concentration range. The magnetovolume effect is also in good accordance with the predictions of Takahashi's theory, even quantitatively.
TL;DR: In this article, the authors measured the pressure dependence of T c for superconducting Tl-Ba-Ca-Cu-O compounds and found that the pressure coefficients change the sign from positive to negative with a maximum T c and that highly hole-doped Tl 2 Ba 2 CuO 6 compounds show a large negative value of d T c /d P.
Abstract: The pressure dependence of T c for the superconducting Tl-Ba-Ca-Cu-O compounds has been measured. It is found that the pressure coefficients of T c in Tl 2 Ba 2 CaCu 2 O 8 change the sign from positive to negative with a maximum T c and that the highly hole-doped Tl 2 Ba 2 CuO 6 compounds show a large negative value of d T c /d P . These results revealed a new feature of the pressure dependence of T c in the hole-doped superconductors and can be interpreted speculatively in terms of the hole concentration in the CuO 2 planes assuming that the carrier concentration is redistributed with pressure.
TL;DR: In this article, the authors present fundamental dynamic equations describing collective diffusive motions of deformed polymers, and incorporate Doi's recent idea on the polymer diffusion in flow, which turns out to be different from those previously proposed by the present author (Phys. Rev. Lett. 62 (1989) 2472).
Abstract: We present fundamental dynamic equations describing collective diffusive motions of deformed polymers. If we incorporate Doi's recent idea on the polymer diffusion in flow, the equations turn out to be different from those previously proposed by the present author (Phys. Rev. Lett. 62 (1989) 2472). In the absence of flow, on the other hand, they are consistent with a theory of Brochard and de Gennes. A seriously ambiguous assumption in the derivation remains.
TL;DR: In this article, the energy band structure of the heavy-electron CeSn 3, known as the heavy electron system having the Kondo temperature of about 200 K, was calculated by a self-consistent relativistic APW method with the exchange and correlation potential in the local density approximation.
Abstract: Based on an itinerant-electron model for the 4f electrons, the energy band structure is calculated for CeSn 3 , known to be the heavy-electron system having the Kondo temperature of about 200 K, by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. An itinerant-electron model assures that this compound is a compensated metal. The large, nearly spherical hole sheet of the Fermi surface explains one of the major frequency branches of the de Haas-van Alphen effect of the order 10 7 Oe. The electron sheet is essentially spherical but highly distorted by the strong 4f-Sn 5p hybridization. It explains clearly origins of all other major frequency branches. These results support the view that the 4f electrons in the heavy-electron Ce compounds should be treated by an itinerant-electron picture.
TL;DR: In this paper, the magnetoresistance and the de Haas-van Alphen (dHvA) effect in CeSn 3 have been measured in the field up to 150 kOe and at temperature down to 0.45 K.
Abstract: The magnetoresistance and the de Haas-van Alphen (dHvA) effect in CeSn 3 have been measured in the field up to 150 kOe and at temperature down to 0.45 K. The magnetoresistance does not show a tendency to saturate in all field directions. This result claims that CeSn 3 is a compensated metal with an equal carrier concentration of electrons and holes, and electron and hole Fermi surfaces possess no open orbits. In contrast to an uncompensated metal LaSn 3 , the 4 f electrons in CeSn 3 become itinerant electrons. This is consistent with the dHvA data which are almost explained by the modified Fermi surface model based on the result of band calculation where the 4 f electrons are treated the same as the usual s , p , d conduction electrons.
TL;DR: In this article, it was shown that a set of universal boundary relations which give the discontinuities of the electromagnetic field across any regular surface can be written via the distribution concept.
Abstract: In the present paper it is shown that a set of universal boundary relations which give the discontinuities of the electromagnetic field across any regular surface can be written via the distribution concept. All specific boundary conditions are then derived from these universal relations as particular cases. It is also shown that any set of linear relations written on a regular surface can not always be the boundary relations of an electromagnetic field. In the case of monochromatic fields the necessary and sufficient conditions for a set of linear equations to be the boundary conditions are given in three theorems. These theorems are applied to the discussion of the validity of boundary conditions of impedance type and show that such conditions can only be valid at certain critical frequencies.