We present an n-dimensional integrable homogeneous Lotka–Volterra system, which has an (n²−1)-dimensional Lie symmetry algebra. Moreover, a wider integrable family is derived from the structure of the Lie algebra.

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We study the gelation process by simulation of a cluster–cluster aggregation (CCA) model, in which networks of gels are constructed through clustering of two-functional or four-functional monomers. We find that gelation time increases when the initial concentration of monomers decreases, while it decreases when the fraction of four-functional monomers increases. At a small initial concentration, gelation time does not markedly depend on the functionality of monomers. This can be related to the forms of clusters: for a large functionality case, the clusters should be tight and should aggregate into compact structures, while for a small functionality case, clusters should form linear chains so that they can easily associate with each other. Numerical observations are compared with experimental results on gelation time for the two types of silica gels under acidic and basic conditions.

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In this work, we have theoretically studied the imbibition process in a cylindrical capillary under a constant, longitudinal temperature gradient, G. A closed-form analytical solution has been obtained and the Washburn law (valid for the isothermal case) has been found to hold for G=0. The space and time evolution of the interface is strongly dependent on surface tension and the viscosity with temperature. By using reported data for an organic oil (squalene), we showed how imbibition can be accelerated when the temperature gradient is negative.

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The spectra of the squares of velocity quadratics including the energy dissipation rate ε per unit mass, the enstrophy ω² and the pressure p were measured using the data obtained from direct numerical simulations (DNSs) of incompressible turbulence in a periodic box with number of grid points up to 2048³. These simulations were performed using the Earth Simulator computing system. The spectra for ε, ω² and p exhibited a wave number range in which the spectra scaled with the wave number k as ∝k^−a. Exponent a for p was about 1.81, which is in good agreement with the value obtained by assuming the joint probability distribution of the velocity field to be Gaussian, while a values for ε and ω² were about 2/3, and very different from the Gaussian approximation values.

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We have investigated the structural properties of the photo-induced metastable phase of a Prussian blue analogue (Na_0.42Co[Fe(CN)₆]_0.78·4.64H₂O), which shows the photo-magnetization phenomenon, as revealed by means of the high angle-resolved synchrotron-radiation X-ray powder diffraction technique. We have found that (1) the structural domain size is larger than the quenched high-temperature phase and (2) the lattice constant a (=10.287(1) Å) is larger than that of the quenched phase (a=10.187(3) Å). These observations indicate that photo-excitation coherently increases the size of the photo-induced metastable region even at low temperature (91K<<T_c).

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We investigate the morphology and kinetics of microphase separation of diblock copolymers where each chain consists of a rod-like block and a flexible block. Simplified phenomenological model systems are introduced, which are coarse-grained in terms of the local concentration of blocks and the local director field of the rod part. Computer simulations of this set of time–evolution equations in two dimensions show that existence of the rod blocks drastically affects the structures of microphase-separated domains due to the elastic energy in the rod-block-rich domains.

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We investigate and discuss the interaction of a hydrogen atom (H) with graphene based on the density functional theory (DFT). Our calculation results show that reconstructions of carbon atoms play an important role in the H adsorption on graphene. When constituent carbon atoms are held rigid, endothermic H adsorption is about 0.2 eV, and the activation barrier is 0.3 eV for H adsorption, due to the strong π-bonding network of the hexagonal carbon. On the other hand, when carbon atoms are allowed to relax, the carbon atom directly below the H atom moves 0.33 Å upward towards the gas phase, and an sp³-like geometry is formed between the H and carbon atoms of graphene. This relaxation stabilizes the hydrogen–carbon interaction, and the exothermic hydrogen adsorption on the graphene has a binding energy of 0.67 eV. We also show that the effective pathway for H adsorption on graphene, which gives an activation barrier for the H adsorption on graphene of 0.18 eV.

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We consider the electronic and magnetic properties of the nanographite ribbon with zigzag edges under periodic or Möbius boundary conditions. The zigzag nano-graphite ribbons possess edge localized states at the Fermi level, which cause a ferrimagnetic spin polarization localized at the edge sites even in a very weak Coulomb interaction. The imposition of the Möbius boundary conditions makes the system a non-AB-bipartite lattice, and depresses the spin polarization, resulting in the formation of a magnetic domain wall. The width of the magnetic domain depends on the Coulomb interaction and decreases with increasing U⁄t.

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Neutron diffraction experiments on the heavy-fermion superconductor PrOs₄Sb₁₂ revealed that a small antiferromagnetic moment, parallel to [010] (y-direction), is induced in the field-induced phase (H||z). The analysis, based on the Γ₁ singlet ground state crystal field model, shows that antiferro-order of O_yz-type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs₄Sb₁₂ is the Γ₁ singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

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Resonant X-ray scattering experiments have been performed on perovskite manganite La_0.5Sr_0.5MnO₃ thin films, which are grown on three distinct perovskite substrates with a coherent epitaxial strain and have a forced ferro-type orbital ordering of Mn 3d orbitals. Using an interference technique, we have successfully observed the resonant X-ray scattering signal from the system having the ferro-type orbital ordering and also revealed the energy scheme of Mn 4p bands. For the forced ferro-type orbital ordering system, the present results evidence that the resonant X-ray scattering signal originates from the band structure effect due to the Jahn–Teller distortion of a MnO₆ octahedron, and not from the Coulomb interaction between 3d and 4p electrons.

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The DC Josephson current through a nano-graphite ribbon placed between two conventional superconductors is theoretically studied by using thermal Green function techniques based on the tight binding model. The electronic states of nanographite ribbons strongly depend on the shapes of their edges, and give a single channel for the electron transport. The nanographite ribbons with zigzag boundaries have partly flat bands due to the edge states, in which the low-energy energy spectrum is a power function of ribbon width. The power-law partly flat bands induce the dependence of ribbon width on both the length dependence of the DC Josephson current and the coherence length. Also, because Andreev bound states highly accumulate close to the zero-energy level, the exponential decay of the DC Josephson current at the zero-energy level to the junction length strongly persists at very low temperatures.

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Pressure-controlled switching between an insulating state and a superconducting state has been successfully realized on a supramolecular organic conductor θ-(DIETS)₂[Au(CN)₄] [DIETS = diiodo(ethylenedithio)diselenadithiafulvalene]. Strong contact between iodine on the donor (DIETS) molecule and nitrogen on the anion [Au(CN)₄] genetates characteristic uniaxial strain effects on transport properties. Under the ambient pressure, the present system undergoes a semiconductor–insulator transition at 226 K. The effect of strains parallel to the conduction plane (ab-plane) is very small. Even under uniaxial strains up to 20 kbar along the a- and b-axis directions, the transition is not suppressed. Surprisingly, however, the c-axis strain induces a superconducting state with T_c of 8.6 K at 10 kbar. Band parameter calculation and the conductivity anisotropy ratio suggest that an increase in the bandwidth W associated with a c-axis strain transforms the system to the metallic and superconducting states. In the metallic state under c-axis strain, the temperature (T) dependence of the Hall coefficient (R_H) and the Hall angle (θ_H) is expressed as R_H∝T⁻¹ and cotθ_H∝T².

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Electronic evolution from an antiferromagnet to a high-T_c superconductor is revealed by angle-resolved photoemission experiments on tetragonal Ca_1.9Na_0.1CuO₂Cl₂ single crystals, which were successfully grown for the first time under high pressures. In this underdoped superconductor, we found clear fingerprints of the parent insulator: a shadow band and a large pseudogap. These observations are most likely described by a “chemical potential shift”, which contrasts clearly with the prevailing wisdom of the “pinned chemical potential” learned from the prototype La_2−xSr_xCuO₄, demonstrating that the route to a high-T_c superconductor is not unique.

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We study phase transition between two topologically different gapped states in the spin-1⁄2 bond-alternating two-leg Heisenberg ladder by investigating string order parameters and the level-crossing method based on the exact diagonalization. We determine the phase diagram on the plane of the bond-alternation δ and the rung-leg coupling ratio J_⊥⁄J, and conclude that the boundary is given as J_⊥⁄J∝δ^2⁄3 in the weak coupling region J_⊥⁄J, δ<<1.

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Neutron elastic scattering measurements have been performed under a hydrostatic pressure in order to investigate the spin structure of the pressure-induced magnetic ordering in the spin gap system TlCuCl₃. Below the ordering temperature T_N=16.9 K for the hydrostatic pressure P=1.48 GPa, magnetic Bragg reflections were observed at reciprocal lattice points Q=(h,0,l) with integer h and odd l, which are equivalent to those points with the lowest magnetic excitation energy at ambient pressure. This indicates that the spin gap closes due to the applied pressure. The spin structure of the pressure-induced magnetic ordered state for P=1.48 GPa was determined.

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⁷⁵As NQR/NMR studies were performed to investigate the successive phase transitions found recently, the gap formation and their interplay in a Kondo semiconductor CeRhAs. NQR/NMR spectra in their respective phases change, reflecting lattice modulation modes, q₁=(0,\\frac12,\\frac12), q₂=(0,\\frac13,\\frac13) and q₃=(\\frac13,0,0). In particular for well-resolved three NQR lines corresponding to the q₃ mode in the lowest temperature phase, the nuclear spin–lattice relaxation rate (T₁T)⁻¹ shows an activation type T-dependence, suggesting a gap opening over the entire Fermi surface, in contrast to the V-shaped gap in isostructural CeNiSn and CeRhSb. The evaluated gap of 272 K and the bandwidth of about 4000 K are one order of magnitude larger than those in CeNiSn and CeRhSb. A lattice modulation forms a gap different from the V-shaped gap.

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The summation of zero-point energies defined by ∑_m,n(π⁄2)\\sqrt(n+β)²⁄a²+m²⁄b² is studied. The parameter β is a positive real number and the zero-point energy of a massless scalar field is given by setting β=0 as a special case. The Casimir energy is obtained by the generalized Abel–Plana formula as a function of β and it is found that the Casimir energy density in the limit b→∞ changes from negative to positive as increasing β. The Casimir effect in the three dimensional case is also considered.

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We study the superfluid–Mott insulator (SF–MI) transition of a spin-1 boson system in an optical lattice, especially the responce of the system to an external magnetic field. Using the mean field theory, we obtain the phase diagram of SF–MI transition at zero temperature. For antiferromagnetic bosons, the Mott insulator region is stabilized when the number of particles per site is even. We find that only by changing the external magnetic field, the SF–MI transition is realized. On the other hand, the ferromagnetic case perfectly recovers the spin frozen case, that is already performed in experiments.

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Nonequilibrium energy transport phenomena are studied using molecular dynamics simulation. The system is made of hard-core particles which contact with the heat baths at the both ends: hot at left end, and cold at right end. In case of fluid, normal (Fourier-type) heat conduction is reproduced in three-dimensional system, but it is not observed in lower-dimensional systems. In solid–fluid coexisting state, the property of energy transport is different between each phase. Fourier-type heat conduction is reproduced, but the solid phase has larger thermal conductivity than the fluid phase. When hydrodynamic shear is induced at hot end, temperature profile of fluid phase is parabolic form but that of solid phase is straight one. These results suggest that continuum description can be applicable to much shorter length scales (for example, micrometer- or nanometer-scale technology) and in contrast, molecular dynamics approach in such scale systems can be used to study nonequilibrium macroscopic phenomena.

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Two-color two-step laser resonance ionization spectroscopy (RIS) was used to study autoionization states of neutral samarium atom (Sm I). Optogalvanic signals were detected from a Sm hollow cathode lamp which was used as an atomic source. Several metastable states of the ground state term were populated from the heated hollow cathode. The six intermediate states which had mutually different total angular momentum (J) values from 1 to 6 were excited using the first step dye laser from the ground state (J=0) and three metastable states having J values of 3, 4 and 5. These six excitation channels were used to study systematically the autoionization states having the probable J values from 0 to 7. The 359 even-parity autoionization states were found and their J values were estimated. The 357 states among the 359 autoionization states were newly found in this experiment.

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Absorption spectrum of the evanescent light at a glass/Rb vapor interface has been observed with atom density from 9×10¹⁹ m⁻³ to 5×10²⁰ m⁻³. Absorption is as high as 60% at the peak of a hyperfine structure split line. The absorption spectrum of the experiment is compared with that of the calculation based on Fresnel’s relation on the assumption of a homogeneous electric susceptibility of the vapor. Near the critical angle the calculation which incorporates the Lorentz–Lorenz local-field correction reproduces the experimental red shift only partly.

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A semiclassical method is adopted to solve the close coupling equations the proton-impact l-mixing collisions between the n=2 fine-structure levels of hydrogenic ions. By use of the semiclassical method, the cross sections in a quantal calculation are well reproduced, and the calculation becomes efficient and tractable. Behaviors of the total and partial cross sections are discussed in detail.

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Total electron scattering cross sections for CF₄, C₂F₆ and C₃F₈ have been measured in the energy range between 1.25 eV and 3000 eV using a compact linear transmission apparatus. Electrons scattered into a narrow forward angular range that should be counted in the scattered one were estimated utilizing measured quantities. The present results for CF₄ agree well with available data at low and high energies, while some discrepancies were seen at intermediate energies. Measured results for C₂F₆ and C₃F₈ were shown at high energies for the first time. Upper bound of the elastic cross sections for these molecules were estimated at electron energies higher than 20 eV.

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We analyze the transport properties of a set of symmetry-breaking extensions of the Chirikov–Taylor Map. The spatial and temporal asymmetries result in the loss of periodicity in momentum direction in the phase space dynamics, enabling the asymmetric diffusion which is the origin of the unidirectional motion. The simplicity of the model makes the calculation of the global dynamical properties of the system feasible both in phase space and in controlling-parameter space. We present the results of numerical experiments which show the intricate dependence of the asymmetric diffusion to the controlling parameters.

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The onset of periodic behavior in a two-dimensional unsteady flow past a rotationally oscillating circular cylinder is examined numerically by the finite-element method. The main emphasis is placed on the wake–cylinder response for the high oscillation frequency. The frequency responses are examined by measuring the power spectra of the lift coefficient. It is shown that rotary oscillations produce a coupled wake–cylinder response. The power spectra of the lift coefficient associated with these coupled motions have dominant peaks which are combinations of multiples of the shedding frequency and the forcing frequency. Instantaneous vorticity contours are also displayed to show the near-wake flow structure subjected to the controlled forcing.

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Preferential acceleration of ³He ions by H cyclotron waves excited via nonlinear effects of strong current-driven instabilities is studied. The plasma is assumed to consist of electrons, H, ⁴He and ³He ions with the abundance of ³He being very small. First, by means of a two-dimensional, electrostatic, particle simulation code, it is demonstrated that ³He ions are selectively accelerated by fundamental H cyclotron waves with frequencies ω\\simeq2Ω_3He (Ω_3He is the cyclotron frequency of ³He). These waves grow to large amplitudes in a plasma with the electron temperature parallel to the magnetic field T_e|| higher than the ion temperature T_H. Next, frequencies and growth rates of H cyclotron waves in a plasma with T_e||>T_H are studied theoretically and numerically. The condition under which the waves with ω\\simeq2Ω_3He become dominant is investigated. It is found that these waves have the greatest growth rates for a large region of the plasma parameters; T_e||⁄T_H\\gtrsim10 mush be satisfied. It is then suggested that these waves can play an essential role in ³He rich events in solar flares.

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The dynamic behavior of the optogalvanic effect in neon hollow cathode discharge using continuous wave diode laser is described. The optogalvanic signal can be subdivided into two types, which show characteristic difference in the metastable atomic density. The polarity and the magnitude of peak of the optogalvanic signal has close relation to change of the lowest metastable atom density.

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Crystal structure of H₃NCH₂COOH·H₂PO₃ was studied in the paraelectric phase (P phase) at 298 K and in the ferroelectric phase (F phase) at 170 K by means of the single crystal neutron diffraction. Two independent protons in the hydrogen bonds forming the H(HPO₃)⁻ chains are disordered over two sites with the separations of 0.486(3) and 0.474(5) Å in the P phase. In the F phase, they are ordered at a position nearly equal to one of two sites related by the disorder. With the proton order, lengths of the P–O bonds with the oxygens involved in the hydrogen bonds forming the chain deviate from their values determined in the P phase. A possible mechanism for the appearance of the spontaneous polarization is discussed in connection with the deformation of the HPO₃²⁻ anions in the F phase.

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According to the adiabatic approximation atoms moving in a magnetic trap keep their magnetic states. We investigate the validity of this approximation for quantum condensates, where a change of field’s direction generates effective interactions between hyperfine angular momentum states. Condensates in general traps are found to be stable because they are confined in the vicinity of the trap center. A decay of a condensate is observable in a trap with extremely large field gradient.

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Phase transitions in dicalcium barium butyrate, Ca₂Ba(C₃H₇COO)₆ (DBB), have been studied by dielectric measurements. At atmospheric pressure, two first order phase transitions are detected at 325 K (I–II transition) and 212 K (II–III transition). A dielectric relaxation with the activation energy of about 0.21 eV is observed in the lowest-temperature III phase. Effect of hydrostatic pressure on the phase transitions was measured and the pressure–temperature (p–T) phase diagram was obtained. The initial pressure coefficients of the I–II and II–II transition temperatures are 0.50 K/MPa and 0.08 K/MPa, respectively. Two pressure-induced phases, IV and V, were found. Unlike to the corresponding propionate crystal Ca₂Ba(C₂H₅COO)₆ (DBP) none of the pressure-induced phases show ferroelectric activity.

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Through far-infrared (FIR) magneto-optical absorption measurements we have investigated excited states of shallow donors in bulk n-InP at 4.2 K. By utilizing advantage of thick bulk samples we have observed transitions from 1s ground state of donors to various excited states as 2p₊₁, 3p₊₁ and 3d₊₁ and a series of oscillatory absorptions caused by transitions to magnetically-induced states. By the optical saturation effect it is found that comparatively weak absorptions as the oscillatory ones become prominent due to suppression of strong absorptions. In order to make clear the excited states of donors under a magnetic field signals due to the 1s–3p₊₁ and 1s–3d₊₁ transitions are extremely helpful, since the resonance positions and the peak heights include various informations for excited states. Based on variation of the oscillation peaks with increases in donor concentration, we conclude that the oscillatory absorptions originate in transitions from the 1s ground state to impurity bands.

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A new LDA+U band calculation is performed on the Kondo insulator material YbB₁₂ and an energy gap of about 0.001 Ryd is obtained. Based on this, a simple tight-binding model with 5dε and 4f Γ₈ orbitals on Yb atoms and the nearest neighbor σ-bonds between them is constructed with a good agreement to the above the LDA+U calculation near the gap. The density of states is also calculated and the shape is found to be very asymmetric with respect to the gap. A formation mechanism of the gap is clarified for the first time in a realistic situation with the orbital degeneracies in both conduction bands and the f states. This model can be a useful starting point for incorporating the strong correlation effect, and for understanding all the thermal, thermoelectric, transport and magnetic properties of YbB₁₂.

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The electronic structures of (Pb₂Cu)Sr₂Eu_xCe_n−xCu₂O_2n+6 (n=2,3) compounds which have fluorite blocks between two adjacent CuO₂ layers have been studied by using ab-initio method. It is found that the anisotropy is enhanced by inserting the fluorite blocks. The Fermi velocity perpendicular to the CuO₂ layers decreases as the thickness of fluorite blocks increases. The Eu substitution is found to affect both the atomic positions and electronic structures. The distance between apical oxygen and copper becomes shorter by the Eu substitution. The energy bands derived from oxygens in the fluorite blocks approach Fermi energy as the content of Eu substitution increases.

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The hydrogen-induced changes in the electronic structure of Pd have been investigated by Compton scattering experiments associated with theoretical calculations. Compton profiles (CPs) of single crystal of Pd and β phase hydride PdH_x (x=0.62–0.74) have been measured along the [100], [110] and [111] directions with a momentum resolution of 0.14–0.17 atomic units using 115 keV x-rays. The theoretical Compton profiles have been calculated from the wavefunctions obtained utilizing the full potential linearized augmented plane wave method within the local density approximation for Pd and stoichiometric PdH. The experimental and the theoretical results agreed well with respect to the difference in the CPs between PdH_x and Pd, and the anisotropy in the CPs of Pd or PdH_x. This study provides lines of evidence that upon hydride formation the lowest valance band of Pd is largely modified due to hybridization with H 1s-orbitals and the Fermi energy is raised into the sp-band.

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For the organic conductor θ-(TMET-TTP)₄PF₆ (TMET-TTP: 2-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-5-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene), electrical resistance has been measured under the uniaxial strain applied along the a-, b-, and c-axes as well as under hydrostatic pressure. Contrary to the prediction of the universal phase diagram in which the c-axis strain will raise the metal–insulator transition temperature by expanding the dihedral angle, the insulating state is suppressed under the strain in all directions. The results are interpreted in terms of the increasing intra-stack transfer integral in the large dihedral angle region.

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The dephasing due to spin–wave excitations is studied for ferromagnetic wires of mesoscopic dimensions in the diffusive regime. The spin–wave dephasing time τ_φ for conduction electrons is calculated as a function of temperature T on the basis of the s–d interaction model. It is shown that in the absence of an external magnetic field, the spin–wave dephasing in some cases becomes comparable to, or even dominates, the ordinary dephasing due to Coulomb interactions. It is also shown that if a magnetic field H is applied parallel to the wire, the spin–wave dephasing is exponentially suppressed with the increase of H at the low-temperature regime of γH>>T (γ: gyromagnetic ratio). This strong H-dependence can be used to examine the influence of the spin–wave dephasing on quantum interference corrections.

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We have studied electronic and magnetic properties of Co/Pd(111) by means of spin- and angle-resolved photoelectron spectroscopy. The perpendicular magnetic anisotropy (PMA) was observed in Co films below 3.5 ML, above which the magnetization direction changes from perpendicular to parallel to the surface. It was found that a simple model calculation based on magnetocrystalline anisotropy qualitatively well explains the emergence of the PMA in Co/Pd(111), where the strong hybridisation between Co 3d and Pd 4d states at the interface plays a crucial role. The re-orientation of the magnetization direction observed in Co films over 3.5 ML is due to the result of the increase of Co 3d electrons with orbital moment parallel to the surface as the Co film thickness increases.

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Sato and the present authors have developed a theory where effects of the 2D superconducting fluctuations in a weak coupling case on the Cooper pairing susceptibility χ(q,ω) and the single particle Green’s function are examined by taking account of the most divergent contributions to those. It has been shown that χ(0,0) diverges as T^{(−T_F⁄2T)}⁄log|T_F⁄T| at T→0, where T and T_F are temperature and the Fermi temperature, respectively. In the present study, we extend the theory to be applied to strong coupling cases and examine roles of the weak three dimentionality leading to a finite value of superconducting transition temperature T_c. We show that T_c is more strongly suppressed in a stronger coupling case. We also examine effects of 2D superconducting fluctuations on the electrical conductivity and show that both of self-energy corrections leading to the pseudogap and vertex corrections such as the Aslamasov–Larkin and the Maki–Thompson terms play their own crucial roles to determine the critical behaviours.

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Nuclear magnetic resonance (NMR) measurements of ⁵⁹Co and ¹⁴N in CoN with a zincblende type structure were carried out in the temperature range from 4.2 K to room temperature. NMR Spectra of ⁵⁹Co are obtained from Free Induction Decay (FID) signals in a static field of 6.3068 T. NMR Spectra of ¹⁴N are obtained by spin–echo method in the same static field. The temperature variations of Knight shifts are derived from resonance peak positions at various temperatures. In this experiment, it is found that the temperature variations of Knight shifts are very small. Therefore, it is concluded that the compound CoN has Pauli paramagnetism. This is consistent with the result of the temperature-independent susceptibility.

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A high field magnetization technique is applied to study the field-dependent behaviors of the molecular magnet, dodecanuclear Iron(III) ring cluster [Fe(OCH₃)₂(dbm)]₁₂, in which twelve numbers of Fe³⁺ (S=5⁄2) ions form a finite chain ring, where dbm = dibenzoylmethane. The low-lying states of the spin manifold are dramatically revealed by the observation of magnetization process using pulsed high magnetic field up to 55 T at temperature down to 0.1 K. We observed four distinct magnetization steps with nearly equal field separation of 10 T, arising from energy-level crossings for the discrete quantum states in the finite spin system. We discuss the structure of energy levels and the relaxation phenomena in the magnetization process around the level-crossing fields. It is found that the anomalous magnetization curve observed at 1.3 K, showing an unusual shape with characteristic hysteresis for increasing and decreasing field, is well reproduced by Phonon Bottleneck effect caused by the week heat exchange between sample and liquid-He bath during the fast field passage. Our results are compared and discussed with those obtained in the other iron magnets showing the step-like magnetization process due to quantum discrete energy levels.

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We have observed a large magnetovolume effect in a melt spun Gd-rich amorphous magnet Gd₆₇Ni₃₃. The magnet shows the forced volume magnetostriction of a positive value of 3.76×10⁻⁵ T⁻¹ at 4.4 K, which is almost as same as that of a typical Invar alloy Fe₆₅Ni₃₅, and the spontaneous volume magnetostriction of 1.97×10⁻³ at 6.9 K. Both volume magnetostrictions are proportional to the square of temperature. They are explained in the framework of spin fluctuation theory for weak itinerant electron magnets. The effect supports that the Ni constituent has a magnetic moment in the amorphous phase with such a low Ni concentration unlike crystalline Gd–Ni compounds. We propose a simple relation of estimating the magnetic moment which causes the magnetovolume effect. It gives the Ni moment of 0.61 μ_B per atom at 0 K and the magnetovolume coupling constant of 1.20×10⁻¹⁴ A⁻²m². We also discuss the arrangement of the magnetic moment in the ground state.

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We study the one-dimensional Hubbard model with next-nearest-neighbor hopping by means of the numerical diagonalization for finite-size clusters. It is found that the ground state is evidently partially spin-polarized in a wide region of intermediate values of on-site Coulomb repulsion, which provides the first example as a minimal model without orbital degeneracy. Analysis of correlation functions makes it clear that the partially spin-polarized states form a spin polaron. Polaron’s size grows with the increasing interaction.

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The pseudo two-dimensional (2D) magnetic systems (LaS)_1.14[M_x(NbS₂)₂] (M = Mn, Fe, Co) were synthesized for the first time, and their magnetic and transport properties were investigated. (LaS)_1.14[M_x(NbS₂)₂] show three-dimensional (3D) magnetic transitions at 4.4, 6.2 and 15 K for M = Mn, Co and Fe, respectively. The 3D transition temperatures are lowered by the quasi-2D magnetic property brought about the insertion of the extra layer LaS to the layered magnets M_xNbS₂, and the 2D short-range order effects are observed in the heat capacity at much higher than the transition temperatures. The minimum behavior of ρ and the maximum behavior of R_H appear in the low temperatures. We consider that the weak localization in the quasi-2D transport system causes the anomalous behaviors of the transport properties.

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The phase diagram and local structure of La_0.7Ca_0.3−xBa_xMnO₃ (x=0;0.03;0.06;…;0.3) lanthanum manganites were studied. The Curie temperature, T_c, of the compositions showed a sharp change near the concentrational structural orthorhombic–rhombohedral phase transition. Maximums of dispersion, σ_Mn–O², and asymmetry, σ_Mn–O³, of pair distribution function for the Mn–O bond distances of MnO₆ octahedron on x-dependence were observed by extended X-ray absorption fine structure (EXAFS) analysis. The maximum of σ_Mn–O² is caused by increase of dynamic rms displacements of Mn–O bond distances near the T_c. The observed x dependence of σ_Mn–O³ reflects the reduction of charge carriers mobility at approaching to T_c.

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We study the effects of hole doping on a two-dimensional antiferromagnetic spin model for the Kondo insulator, where the spin liquid phase and the magnetically ordered phase compete each other. By means of the self-consistent Born approximation within the bond operator formalism as well as the standard spin wave theory, we discuss dynamical properties of a doped hole around the quantum critical point. It is clarified that a quasi-particle state stabilized in the spin liquid phase is gradually obscured as the system approaches the quantum critical point. This is also the case for the magnetically ordered phase. We argue the similarity and the difference between these two cases.

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Excitations and neutron scattering spectra in the antiferro-quadrupolar ordering phase of CeB₆ are studied theoretically. We develop a general formulation of the boson expansion method of multipoles and clarify the selection rules governing the multipolar dynamics. We apply the method to the RKKY model, which was introduced before for this material, and discuss the dispersions of excitation energies and their dependence on the magnetic field. Then neutron scattering spectra are calculated within the dipole approximation and compared quantitatively with the experiments by Bouvet. Possible interpretations of the peak structures in the observed spectra are discussed in connection with the characteristic multipolar interactions in CeB₆.

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Various physical properties of the pyrochlore oxide Y_2−xBi_xIr₂O₇ have been studied. The magnetizations M measured under the conditions of the zero-field-cooling (ZFC) and the field-cooling (FC) have different values below the temperature T=T_G. The anomalous T-dependence of the electrical resistivities ρ and the thermoelectric powers S observed at around T_G indicates that the behavior of the magnetization is due to the transition to the state with the spin freezing. In this spin-frozen state, the Hall resistivities ρ_H measured with the ZFC and FC conditions are found to have different values, too, in the low temperature phase (T<T_G). Possible mechanisms which induce such the hysteretic behavior are discussed.

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We report unambiguous microscopic evidence from ³¹P NMR under H_ext≅7.3 T for significant ionic disorder in the Yb³⁺ chain in Yb₄(As_1−xP_x)₃ (x=0.05 and 0.40), which have similar characteristic χ(T) and C_p(T,H_ext) behavior to the antiferromagnetic quantum spin chain (AFQSC) system Yb₄As₃. Our conclusion is based on the observations only below the charge–ordering transition at T₀≅292 K of clear structures in the spectrum, which can be fitted well by the superpositions of almost equally spaced five Gaussian components. Since perfect ordering of Yb³⁺ in the chain sites would lead to a single-line spectrum also below T₀, the structures should be ascribed to significant ionic disorder in the Yb³⁺ chain and resulting distribution of local configurations of Yb³⁺ in the eight nearest-neighboring Yb sites around ³¹P. Quantitative comparisons with a simple model show that about 1/3 and at least 10% of the chain sites are disordered, namely occupied by Yb²⁺, for x=0.40 and 0.05, respectively. Combining with previous other experimental results, extreme robustness against the disorder in the Yb³⁺ chain is deduced for the characteristic χ(T) and C_p(T,H_ext) behavior normally attributed to the AFQSC.

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We have investigated the dependence of lasing modes of dye-doped microdroplets on dye concentrations. Single droplets were confined in an ion trap and irradiated by a pulsed green laser. Polarization characteristics of both emission spectra and microscopic images were obtained for various dye concentrations. As the concentration decreases, the laser lines shift toward shorter wavelength and the structures of the spectra become more complicated while microscopic spatial images changed drastically. Polarization analyses have revealed that, at the most dilute concentration, only lasing with polarization perpendicular to the radial direction occurs in a droplet.

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Formulation of the transmission and reflection of light in terms of vector cylindrical waves is given for two-dimensional photonic crystals having complex unit cells which contain two or more rods in a unit cell. Some examples of the numerical calculations using the supercell method are given for arrays of cylinders which have impurities or defects. It is shown that the computed transmittance for a multilayer with periodic impurities agrees very closely with the band-structure calculation of the impurity band. We also examined the waveguide effect of the line defect in a photonic band gap, and demonstrated the possibility of using this method in the design of defect waveguides.

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