Non-crossing random walkers with attractive interactions called friendly walkers (FWs) are studied. A restriction on trajectories, which is analogous to Pauli's exclusion principle, is imposed and the Fermi partition functions are defined. We prove a theorem that the pair connectedness of the bond directed percolation (DP) with bond concentration p is related to the Fermi grand partition function of FW if we set the temperature T=-1/(k_B ln p) and the chemical potential μ=-i π/ln p, where k_B is the Boltzmann constant and i=√-1. The pure imaginary chemical potential means that the DP transition can be regarded as a symmetry breaking of parity in the number of FWs. As a corollary of the theorem, a new method is proposed for calculating the series expansion of the pair connectedness and percolation probability of DP using the low-temperature expansion data of FW.

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We consider whether two rigid plates (on a hinge) swinging completely symmetrically with respect to the up and down directions can produce enough lift for flight. By simulating a simple flapping motion in two-dimensional space using a discrete vortex method, we found a new type of symmetry-breaking mechanism that allows for the generation of sufficient lift to realize steady-flapping flight. The most important factor in determining the behavior of the model is the nature of the flow following the second downstroke, in which the wing produces significant lift through its interaction with the separation vortices.

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The metal-insulator transition (MIT) in the thiospinel Cu_1-xZn_xIr₂S₄ has been investigated by means of ⁶³Cu NMR. We find that the sample with x=0.3, having a uniform metallic phase at room temperature, exhibits a phase separation into the metallic and insulating regions below T_MI ∼ 70 K, where the first order MIT is observed in the resistivity data. The insulating regions have the same Cu Knight shift as that in the diamagnetic insulator at x=0. This indicates that the charge density in the low-T insulating phase is invariant, which causes the carriers introduced by the Zn substitution to be segregated from the insulating regions. Based on these observations, a possible mechanism of the MIT is discussed.

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We present a new algorithm for quantum Monte Carlo simulation based on global updating with loops. While various theoretical predictions are confirmed in one dimension, we find, for S=1 systems on a square lattice with an antiferromagnetic biquadratic interaction, that the intermediate phase between the antiferromagnetic and the ferromagnetic phases is disordered and that the two phase transitions are both of the first order in contrast to the one-dimensional case. It is strongly suggested that the transition points coincide with those at which the algorithm changes qualitatively.

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Based on the tight binding method with a hopping integral between the nearest-neighbor atoms, an oscillator strength ∫₀^∞ d ω Re σ (ω) is discussed for armchair and metallic zigzag carbon nanotubes. The formulae of the oscillator strength are derived for both types of nanotubes and are compared with the result obtained by a linear chain model. In addition, the doping dependence is investigated in the absence of the Coulomb interaction. It is shown that the oscillator strength of each carbon nanotube shows qualitatively the same doping dependence, but the fine structure is different due to its own peculiar band structure. Some relations independent of the radius of the tube are derived, and a useful formula for determining the amount of doping is proposed.

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We study the effect of correlation on the Bragg reflection in the 3D electron gas, the 1D Luttinger liquid, and the 1D Hubbard model in an alternating periodic potential at half-filling. In the last system, we suggest a Luttinger-liquid-type quasimetallic state in the crossover region from the band insulator to the Mott insulator. We explain the appearance of this state in terms of the incompatibility of the Bragg reflection with the concept of Luttinger liquids.

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We study the domain wall (DW) resistivity in a thin wire of disordered ferromagnetic metal, in the presence of an ac magnetic field with the frequency ω_ex applied parallel to the wire. Periodic oscillations of a DW driven by the magnetic field induce spin-flip electron scattering, which increases the resistivity, particularly when ω_ex is nearly equal to the attempt frequency ω₀ of the DW. We calculate the negative correction δ σ to local conductivity due to the spin-flip electron scattering at zero temperature. We find that the correction arising inside the DW region is given by δ σ/σ₀ ∝ -1 /[(1-ω_ex/ω₀)² + (η/ω₀)²], where η is the friction coefficient for the DW motion and σ₀ the Drude conductivity. This result indicates that we can estimate the important parameters ω₀ and η for DW dynamics by measuring the resistivity as a function of ω_ex.

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The lifetime of Shockley states on metal surfaces is calculated under the assumption that the Coulomb interaction between electrons in Shockley states is mainly responsible for the finite lifetime of these states, and that the Coulomb interaction would be screened by the bulk electrons. With single-particle wave functions of Shockley states, the Fourier expansion component of the screened Coulomb potential, V_s, is calculated, and the dependence of V_s on the lattice constant and the width of the projected band gap at the edge of the first Brillouin zone (¯Γ) are investigated. A second-order perturbation calculation with respect to V_s is performed for the self-energy of a single electron in Shockley states, and then the lifetimes of these states on Cu(111) and Ag(111) surfaces are evaluated. Our results qualitatively agree with experimental results.

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The vortex structure in superconducting stripe states is studied according to the Bogoliubov-de Gennes theory on the two-dimensional Hubbard model with nearest-neighbor sites pairing interaction. The vortex is trapped at the outside region of the stripe line, where the superconductivity is weak. The superconducting coherence length along the stripe direction becomes long. There are no eminent low-energy electronic states even near the vortex core. These characters resemble the Josephson vortex in layered superconductors under a parallel field.

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An X-ray scattering experiment using synchrotron radiation has been performed on rutile-type β-MnO₂ single crystal. Below T_N, satellites due to magnetic scattering appear, which provides direct evidence of a helical magnetic structure. The wave number of the magnetic helix is approximately 0.297c^*, incommensurate to the lattice and shows very weak temperature dependence. The extinction rule of the satellites is consistent with the magnetic structure proposed by Yoshimori [J. Phys. Soc. Jpn. 14 (1959) 807] in which the nearest helix chains are coupled in an antiferromagnetic way. The temperature dependence of the scattering intensity indicates that the critical exponent β is anomalously small for an ordinary three dimensional antiferromagnet; this strongly suggests a large chiral degeneracy effect of helical magnetism.

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We analyze the angular dependence of the resonance field of ¹¹B-NMR spectrum with respect to the magnetic field in phase II of CeB₆. The experimental results are well explained as a sum of the magnetic dipolar and the transferred hyperfine field from the Ce site. The latter is the microscopic origin of the hyperfine field from the octupolar moment introduced phenomenologically. It is shown that the unusual temperature and magnetic field dependence of the resonance field at low fields in phase II originates from that of the antiferromagnetic moment through the the dipolar field and is consistent with the neutron scattering results.

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Raman scattering of (NH₄)₃H(SeO₄)₂ single crystal has been observed in the frequency range between 700 cm^-1 and 1000 cm^-1 in the temperature region from 219.3 K to 420.7 K. It was found from the present experimental result that the 827 cm^-1 line in phase II of this compound is a new Raman line which is caused by the stretching mode of a single Se-O bond in SeO₄ tetrahedra accompanied by the destruction and reconstruction of hydrogen bonds.

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By means of the perturbative renormalization group method, we study a long-time behaviour of some symplectic discrete maps near elliptic and hyperbolic fixed points. It is shown that a naive renormalization group (RG) map breaks the symplectic symmetry and fails to describe a long-time behaviour. In order to preserve the symplectic symmetry, we present a regularization procedure, which gives a regularized symplectic RG map describing an approximate long-time behaviour successfully.

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The two periodic soliton solution to the Davey-Stewartson II equation is analyzed to show that the periodic soliton resonance exists between them. There are two types of singular interactions: one is the resonant interaction that generates one periodic soliton after collision, while the other is the long-range interaction.

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Free falling atomic laser beams with sufficiently weak inter-atomic interaction are investigated. An approximate solution of one-dimensional Gross-Pitaevskii equation with gravitational potential is obtained by using the WKB analysis. This shows the effects of the inter-atomic interaction on the velocities of bosonic atoms. The analysis is extended to investigate the interference pattern of two atomic laser beams.

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In some practical systems a very short, rapid changing stage appears inside a relatively very long and slowly changing process. Such a system may be called quasi-discontinuous system. In order to qualify it, we quantitatively give the definitions of quasi-discontinuity and quasi-discontinuous region. By a simplified model, we have shown that the scaling law of the averaged laminar length of the intermittency in such systems can be an intermediate one between that of type I and type V. This phenomenon has been observed in Hindmarsh-Rose model describing neuronal activities.

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Simple, completely explicit symplectic integration formula are obtained for the Nosé-Poincaré thermostat; a Hamiltonian dynamics version of the Nosé-Hoover thermostat. The time reversibility holds in each of recursion relations.

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Friendly walkers are the non-crossing random walkers on a lattice with attractive interactions. We characterize each trajectory of friendly walkers by the number of walkers m, the time interval of observation t and the total length of trajectory r. A new algorithm to generate trajectories on a spatio-temporal plane is proposed and the distribution function of number of distinct trajectories characterized by (m, t, r), f_{m, t}(r), is estimated by a random sampling method. The variance, the skewness and the kurtosis of f_m,t(r) converge to finite values without scaling as t → ∞ for each m. The distribution is asymmetric and its tails are expressed by stretched exponential functions. We consider the canonical distribution of m friendly walkers by introducing a parameter p which plays the same role of the Boltzmann factor e^-β in the usual equilibrium systems. We calculate the mean and variance of r in the canonical distribution as a function of p for each m at t. It is observed that the variance of r per unit time interval has a peak at a certain value of p for each m=2, 3, 4 and 5. We discuss the possibility that the peak indicates the phase transition of trajectories of friendly walkers realized on a spatio-temporal plane.

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The equilibrium problem of a liquid metallic drop in the external field produced by two sets of coils (for heating and positioning), carrying currents at different frequencies, in ambient of microgravity has been analytically considered. The free boundary problem resulting from considering infinite conductivity for the drop and its surface tension has been solved almost exactly. The stability of such equilibria with respect to rigid displacements has also been explicitly calculated. Axial and lateral shifts are stable and for rigid rotational displacements restoring torques are also obtained. However, the positioning coils can give unstable contribution if the elongation of the drop is smaller than about two. This can offer an explanation to the some time destroying motion of the drop in TEMPUS experiments when the heating coil was switched off.

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The hydrodynamic interaction between two cylinders with rotational motion through an inviscid and incompressible fluid is investigated theoretically. The dynamical behaviors of an elliptic cylinder moving around a fixed circular cylinder are described based on the dynamical equations of motion in the plane of motion. In a relative coordinate system moving with the stream, the kinetic energy of the fluid is expressed as a function of fifteen generalized added masses due to the planar motion of the two cylinders. By means of the generalized added masses, the planar motion of an elliptic cylinder around a fixed circular cylinder can be computed without considering the flow field. In order to proceed the problem analytically, a set of transformations of harmonics between two corresponding spaces are obtained. These transformations are applied to derive the complete complex potentials by using the successive potential procedure, which is an extension of the circle theorem in two dimensions. These results are utilized to predict trajectories of an elliptic cylinder around a fixed circular cylinder in planar motion and to estimate the effects of non-circularity, initial position and initial velocity on the interaction between two cylinders. The numerical results show explicitly that the dynamical behaviors of the moving bodies with rotational motion appear nonlinear. Their moving properties exhibit significant difference from those in the particle dynamics.

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Behavior of a free viscous liquid sheet subject to a temperature difference between both surfaces is analytically examined by considering the thermocapillary effect. Under the long wave approximation, nonlinear evolution equations of the sheet thickness and velocity are derived for sufficiently small Prandtl number, while a nonlinear relation between the position of sheet centerline and the sheet thickness is obtained. It is shown that the surface profiles deviate from the symmetric (dilational) to the asymmetric with flat troughs and large crests as the temperature difference increases. It is also shown that there exist certain critical temperature difference ΔΘ_c above which the sheet becomes linearly unstable. In the neighborhood of ΔΘ_c, a weakly nonlinear equation of the sheet thickness is obtained and numerically solved for the instability. However, since ΔΘ_c is estimated to be so large in both linear and nonlinear analyses, the sheet may be substantially stable as far as the small Prandtl number is considered.

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Natural convection evolving along a vertical flat plate is considered under (i) isothermal and (ii) uniform-heat-flux plate boundary conditions. Basic flow is assumed to be governed by steady boundary-layer equations. Linear and weakly-nonlinear stability analyses of the basic flow are made with the aid of the Galerkin method in which the field variables are expanded in terms of Chebyshev polynomials. The Stewartson-Stuart equation for the two-dimensional propagating disturbance is derived and its stability is examined for the cases of the Prandtl number Pr = 0.733 (air) and Pr = 6.7 (water). The main results are such that (i) the motion is supercritical over almost all the linearly unstable region except for a narrow boundary region defined by small wavenumbers; (ii) Huerre's criterion shows that the motion is convectively unstable along the most highly amplified path over the whole computed range of the Reynolds number; (iii) Newell's criterion shows that the motion tends to be modulationally unstable at lower values of the Reynolds number especially in air.

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It is both experimentally and theoretically demonstrated that ion flow velocity at an arbitrary angle with respect to the magnetic field can be measured with a directional Langmuir probe. Based on the symmetry argument, we show that the effect of magnetic field on directional probe current is exactly canceled in determining the ion flow velocity, and obtain the generalized relation between flow velocity and directional probe currents valid for any flowing direction. The absolute value of the flow velocity is determined by an in situ calibration method of the probe. The applicability limit of the present method to a strongly ion-magnetized plasma is experimentally examined.

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A general formula for the dispersion characteristics of electrostatic waves in dusty plasmas in the presence of charge fluctuation of dust particles is derived based on the linear response theory. The formula is applicable to arbitrary plasma models and waves. Charging equation due to plasma current on the dust surface is employed to describe the charge fluctuation effect. In particular, temperature fluctuation associated with the space charge fluctuation is taken into account in the charging equation and is found to make an important contribution to the damping or growth of the wave. Stability of low frequency waves where the electron response can be treated as static is discussed in detail. It is shown that the dust charge fluctuation contributes to damping when the dust is negatively charged, but to growth when the dust is positively charged. Results are applied to ion waves with positive dust charge.

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The crystal structure of β-CuBrTe at room temperature has been analyzed by the Rietveld method with X-ray powder diffraction data. It belongs to the orthorhombic system √2a×√2b× 3c (a ≈ b) with the space group Fddd, where the crystal system of the α-phase is assumed as a× a× c. The α-phase of CuBrTe at high temperature has the disordered arrangement of Cu atoms, but the structure of β-CuBrTe includes the ordered arrangement.

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The application of Maximum Entropy Method to the electron density reconstruction in the case of phaseless problem in both centro- and non-centrosymmetric structures is described. The use of specially constructed priors is suggested for a simultaneous refinement of the electron density distribution and phases of the observed structure factors. On an example of GaN data it is shown that a non-uniform prior may be a necessity for arriving at proper reconstruction of the charge density distributions. MEM can be also very sensitive to the positional parameters as demonstrated on the case of FeSi. The use of non-uniform prior helps also to understand the origin of covalent bonding, which is demonstrated on the Si case, for which obtained charge density distribution is in excellent agreement with theoretical predictions.

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Raman scattering from the deuterated compound Rb₃D(SeO₄)₂ single crystal is studied in the temperature range between 79.2 K and 480.0 K. A new Raman line appears at 827 cm^-1 as much as 60 K below the superionic phase transition temperature, and does not depend on temperature and deuteration. It has been suggested that this line is caused by the stretching motion of a single Se-O in SeO₄ tetrahedra accompanied by the destruction and reconstruction of a hydrogen bond. In low temperature region, the dielectric constant of Rb₃D(SeO₄)₂, measured at 100 KHz, shows a λ-type anomaly at 93 K, while the observed Raman spectra are almost the same above and below this temperature.

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Theoretical investigation of the cluster-distortion coupling model is carried out in the low-temperature phases of two typical superionic conductors AgI and PbF₂, which are characterized by two types of phase transitions, 1st-order order-disorder type and Faraday type, respectively. It is found that the static local distortion induced therefrom by clustering of mobile ions is quite consistent with the negative local distortion experimentally obtained from EXAFS measurement in β-AgI, and with the anomalous temperature dependence of the lattice constant of β-PbF₂. The effective interaction energy between mobile ions decreases with temperature due to the static and dynamic distortions. The specific heat and ionic conductivity are also in agreement with experimental observations in both materials.

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Characteristic features in phases of Bose-Einstein condensations (BEC) for systems of two-components in gas phases of Alkali-metal atoms trapped by harmonic potentials are discussed on the basis of numerical calculations by the use of Gross-Pitaevskii equation. Condensations with and without vortices are considered in order to make clear spatial distributions. The shape of spatial distribution is essentially dependent on the ratio of interaction strengths between intra-components and inter-components. We emphasize the possibility of coexistence of vortex-free state (where the angular momentum \ell is 0.) for the one component in BEC and vortex state (\ell_z =1) for another component whose shape is the donut-like spatial distribution. Furthermore, fluctuations of these states are discussed. In partiucular, we concentrate our attention to the appearance of the core modes with \ell_z =0 symmetry for the component with a vortex. In connection with the behavior of the core modes, the contribution of the component without a vortex to the stability of the above vortex is discussed on the basis of numerical calculation.

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Within the framework of two parameter octahedral potential for a dipolar impurity in ionic crystals, it is possible for impurity to possess minimum-energy orientational configurations in two crystallographic directions simultaneously. Two combinations are ‹111›-‹110› and ‹111›-‹ 100›. Taking first model we have tried to explain paraelectric resonance in KI:OH^- system with the effect of electric field. The data give good agreement for backward lines with the experimental data.

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The electronic structure of networked nano-graphites is investigated in relation to the effects of fluorine-introduced sp³-defects on the nano-sized π-electron system. In the low fluorine concentration region, the shrinkage of the π-conjugated system due to introduced sp³-defects reduces the orbital diamagnetism and modifies the electron hopping process between nano-graphite domains, and the edge-inherited non-bonding π-electrons having localized spins, which give a unique feature to nano-sized π-electron system, are seriously affected by the attack of fluorine atoms to edge carbon sites. In the intermediate fluorine concentration region, the spin density is enhanced by dangling bond spins generated by the local destruction of the π-conjugated system at interior carbon sites. The hyperfine-broadening of the linewidth and the reduced spin-lattice relaxation rate in ESR spectra suggest the isolated nature of the fluorine-induced localized spins in contrast to the edge-inherited spins.

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The effect of the Hund's-rule coupling on the Kondo effect is studied in connection with the nature of renormalized quasiparticles. Applying the Wilson numerical renormalization-group method, we investigate a system where two localized electrons at impurity site hybridize with conduction electrons with different strength. It is shown that two characteristic energy scales, T_K1 and T_K2, (T_K1 > T_K2) exist irrespective of the existence of the Hund's-rule coupling due to the orbital dependence of hybridizations. As the Hund's-rule coupling is switched on and increased, the ratio between two characteristic energy scales is much more enhanced with both being decreased. We find widely a region of parameters in which T_K2 cannot be seen in the temperature range accessible by experiments. Practically, the system shows a new type of itinerant-localized duality where one of two localized electrons forms local Fermi liquid with conduction electrons and the other remains as a localized spin. The case of antiferromagnetic Hund's-rule coupling is also discussed. It is shown that the low energy effective Hamiltonian is described by the same form irrespective of a sign of the Hund's-rule coupling.

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The de Haas-van Alphen (dHvA) effect has been investigated on high-quality single crystals of FeP in a double helical magnetic state with a 5c period in the magnetic fields up to 14 T and at temperatures down to 0.42 K. Single crystals were grown by the chemical transport technique using iodine as the transport agent. Nineteen branches were observed in three crystallographic planes (100), (010) and (001), and analyzed with simple analytic equations for the Fermi surfaces. Many of the dHvA branches have a characteristic angular dependence and are found to correspond to the orbits on surfaces beyond the Brillouin zone in the magnetic state which is reduced to 1/5 of the non-magnetic one with the MnP-type along the [001] direction. These branches originate from the orbits caused by a magnetic breakdown phenomenon under high fields. Cyclotron mass ratios were obtained to be up to 5.9, whereas the electronic specific heat coefficient is rather small, 2.86 mJK^-2mol^-1.

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The electric resistivity and magnetic susceptibility have been measured for hexagonal intermetallic compounds R₇Rh₃ (R=Gd, Tb, Dy, Ho, Er and Y). At low temperature, these compounds except Y₇Rh₃ have antiferromagnetic order. In room temperature region, the electric resistivity increases with decreasing temperature in all the compounds and some of these compounds show a broad maximum at paramagnetic region. The pronounced increase of electric resistivity due to superzone gap formation at the Fermi level has been observed at the Néel temperature. These properties could be explained by the semimetallic band scheme.

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We used the Boltzmann equation to calculate the electrical resistivity of the double exchange interaction systems. Starting from the Hamiltonian developed by [Kubo and Ohata's Hamiltonian J. Phys. Soc. Jpn. 33 (1972) 21], we calculated the resistivity due to the spin wave scattering. It was found that below T_C, the behavior of resistivity was quite complicated and most importantly, its magnitude is small compared to experimental results.

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Giant magnetoresistance (-1530%) in NiS was observed under magnetic field 4 T at temperature 268 K. The mechanical is related to a magnetic field-induced magnetic and electrical transition from antiferromagnetic anomalous-metal phase to paramagnetic metal phase below temperature 270 K.

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Magnetic and transport properties of the pyrochlore molybdate R_2-xR_x^′Mo₂O₇ (R, R^′=rare earth, Y), which exhibits the metal-insulator (M-I) transition with varying x, have been studied. The transition from an antiferromagnetic spin-glass state to a ferromagnetic one occurs at x far from the M-I phase boundary, indicating that the intimate correlation of the magnetic state with the conducting nature is not so obvious. In Nd₂Mo₂O₇, the ordering of Mo spins takes place at about 95 K, where the anomalous Hall resistivity appears with decreasing temperature T along with the spontaneous magnetization. With the ordering of Nd moments which becomes significant below ∼20 K with decreasing T, the behavior of the anomalous Hall resistivity markedly changes, while the Mo-magnetization is partially cancelled by the Nd magnetization. It is shown that the anomalous Hall resistivity can be described by two components, 4π R_sM_Mo and 4π R_s^′M_Nd, the contributions from the uniform magnetizations M_Mo and M_Nd of Mo and Nd moments, respectively. The sign of R_s^′ is opposite to that of R_s. Brief arguments are given if the unusual behavior of the Hall resistivity is related with the nonzero chirality of the magnetic moment system.

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We theoretically examine how a vortex-glass transition in type II superconductors due to point disorder is changed by including line-like disorder. With decreasing field, the resulting glass transition line approaches the (linear) BG transition line B_BG(T) of the case with no point disorder, while it deviates upwardly from the BG line with increasing fields and, in high enough fields, approaches the VG transition line B_VG(T) of the case with no line disorder. It is argued that this picture will remain valid in clean systems showing the first order transition and a narrow vortex slush region in intermediate fields, and that the slush region will shrink due to an addition of weak line disorder. It is found that the presence of point disorder makes the resulting critical scaling behavior isotropic and, nevertheless, that the resulting glass phase should have the transverse Meissner effect. Results are qualitatively compared with recent resistivity data, and a phase diagram of clean systems with a lower critical point of the first order transition line is suggested.

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The diamagnetism of a normal metal (N: Cu or Au), which is induced by the proximity effect of a superconductor (S: Nb), has been investigated for N-S double layers, which are formed by a thin-film deposition process. Detailed studies of samples, which have different electronic mean-free path \ell_N in N, suggest that \ell_N should be controlled by the impurity concentration rather than the mechanical imperfections in the lattice in order to clarify the \ell_N dependence of the proximity effect. Both the screening distance ρ in N and the parameter ν in ρ ∝ T^-ν increase with an increase in \ell_N. This result can be understood on the assumption that the normal metal changes its behavior from the “dirty” limit (ξ_N>\ell_N) to the “clean” limit (ξ_N<\ell_N), where ξ_N is the coherence length in N.

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We propose a mechanism of the semiconductive temperature dependence of the c-axis resistivity (ρ_c) in the normal state of high-T_c superconductors. We show that antiferromagnetic spin fluctuations in the CuO₂-layer affect the temperature dependence of the Fermi surface shape and that they decrease (increase) the conductive carrier density (band mass) in the c-direction. Thus, when this effect dominates the temperature dependence of ρ_c, ρ_c increases at low temperatures. On the other hand, in the in-plane direction, the AF spin fluctuations do not affect the carrier density while they decrease the so-called k-mass at low temperatures. As a consequence, taking into account the damping rate which is caused by the electron-electron interaction, we obtain the in-plane resistivity (ρ_ab) which decreases with decreasing temperature. Thus, the present mechanism can explain the semiconductive temperature dependence of ρ_c satisfying the metallic behavior of ρ_ab.

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In the two-dimensional Heisenberg antiferromagnet (C₂H₅NH₃)₂CuCl₄, the intralayer exchange interaction is ferromagnetic, whereas the interlayer exchange interaction, which is less than 10^-4 of the intralayer one, is antiferromagnetic, and the spins collinearly lie in each layer. To investigate the effect of pressure on its spin structure, magnetic susceptibility and neutron scattering measurements under pressures up to 2.5 GPa were performed. The magnetic susceptibility measurements revealed the appearance of a pressure-induced weak ferromagnetic moment along the c-axis around 0.6 GPa. The neutron scattering measurements clarified the noncollinear spin structure which causes the weak ferromagnetic moment mentioned above. That is, the ferromagnetically coupled spins in each layer cant from the layer, which brings about the weak ferromagnetic moment along the c-axis. The ferromagnetic coupling in each layer and the antiferromagnetic coupling among the nearest-neighboring layers are maintained at least up to 2.5 GPa.

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Antiferro-quadrupolar (AFQ) ordering in the cubic Γ ₃ ground state system PrPb₃ has been studied by means of magnetization and specific heat measurements under magnetic fields H. Field variation of the AFQ transition temperature T_Q (0.4 K at H=0) has been determined for the three crystallographic directions ‹100›, ‹110› and ‹111›. The obtained T_Q(H) is strongly anisotropic, with T_Q^‹100›(H) the largest (∼0.7 K at 6 T). The AFQ phase diagram and the magnetization behavior observed for H allel ‹100› are well explained by a model that incorporates both antiferromagnetic and antiferroquadrupolar interactions. The interactions between field-induced staggered magnetic moments stabilize the AFQ order. This simple model, however, seriously fails to explain the observed anisotropy: T_Q^‹100›(H)>T_Q^‹110›(H)>T_Q^‹111›(H). Reconsidering the field-induced multipole moments in the AFQ phase, we propose that inclusion of a weak ferro-octupolar interaction between Γ ₅ type octupole moments is important in reproducing the anisotropic phase diagram of PrPb₃.

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Specific heat and magnetization measurements have been performed with a low carrier heavy fermion compound YbSb. Successive phase transitions at 0.5 K and 5 K were observed by specific heat measurements under external magnetic fields up to 12 T. The transition temperature at 5 K increases with increasing external magnetic field. The magnetization measurements indicate the existence of field induced magnetic ordered moments at 5 K. These magnetic properties of the phase transition at 5 K are discussed in terms of a mixing-typed antiferroquadrupolar ordering model with a Γ₆ Kramers doublet as the crystalline electric field ground state.

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Destabilization of the charge-ordered (CO) state in half-doped manganites by chromium (Cr) doping in the manganese (Mn) sites was investigated. The Cr doping in the half-doped manganites makes the CO state short-ranged and induces new ferromagnetic metallic (FMM) phase at low temperature. Real space images taken in the CO state by electron microscope clearly show coexistence of the short-ranged CO and FMM states, which is characterized as a microscopic-scale phase separation. Furthermore, the CO state in the Cr-doped manganites has a superlattice structure with the incommensurate wave vector q=(1/2-ε)a_o^*, where Ε depends on the Cr concentration. These results suggest that the Cr doping suppresses the incommensurate to commensurate structural transition found in the half-doped manganites and produces new FMM phase.

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The pseudogap phenomena observed on cuprate high temperature superconductors are investigated based on the exact diagonalization method on the finite cluster t-J model. The results show the presence of the gap-like behavior in the temperature dependence of various magnetic properties; the NMR relaxation rate, the neutron scattering intensity and the static susceptibility. The calculated spin correlation function indicates that the pseudogap behavior arises associated with the development of the antiferromagnetic spin correlation with decreasing the temperature. The numerical results are presented to clarify the model parameter dependence, that covers the realistic experimental situation. The effect of the next-nearest neighbor hopping t' is also studied.

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Shubnikov-de Haas effect (SdH) measurements and complementary electrical resistivity and specific heat measurements were performed on a high-quality whisker single crystal of UP₂. All except one of detected branches exhibit angular dependences clearly indicating the Fermi surfaces (FS) of cylindrical form. The effective cyclotron masses were determined to range from 1.9 to 9.3 m₀, which yields an electronic specific heat coefficient of 25 mJ/K²·mol. This is in good agreement with 27 mJ/K²·mol determined directly by the low-temperature specific-heat measurement. As in sister compounds UAs₂, USb₂ and UBi₂, the two-dimensional Fermi surfaces are formed in the flattened magnetic Brillouin zone and the conduction electrons are confined mainly in the U planes. Significant contribution of itinerant 5ƒ electrons to the conduction band is concluded from rather big effective cyclotron masses.

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Neutron diffraction studies have been carried out on a single crystal of the metallic pyrochlore ferromagnet Nd₂Mo₂O₇. The magnetic structures proposed at 4 K is non-collinear for both the Mo- and Nd-moments, where the net moments of the two systems align antiparallel. In the temperature region between the Curie point (∼93 K) and ∼30 K, the moments primarily at Mo sites orders with the ferromagnetic magnetization, where the structure seems to be non-collinear, too. The ordering of the Nd moments gradually develops and becomes significant below ∼20 K with decreasing temperature. Discussion on the relationship between the magnetic structure and the anomalous transport properties is presented.

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Raman-scattering and optical-microscopy studies have been carried out in pure and doped CuGeO₃ crystals under strictly hydrostatic pressure up to about 10 GPa at room temperature by using diamond anvil cell. Anomalies of the mode Gruneisen parameters of the low-frequency phonons are found. In heavily Mg- and Ni-doped crystals successive first-order structural phase transitions of the normal phase (phase I)→the pale-green phase (phase II)→the green phase (phase IV) are observed as the hydrostatic pressure is increased in the first run. The critical pressure of the second phase transition between phases II and IV strongly depends on the dopant concentration, while it does not occur in Si-doped crystal. Upon releasing pressure the samples are transformed from phase IV to the deep blue phase (phase III) which is quenchable down to ambient pressure. Phases III and IV are identified as the phases which probably possess pyroxene structures and have already been reported to emerge in pure crystal only under quasihydrostatic pressure.

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We study a kind of filtering, an amplitude truncation with upper and lower truncation levels x_max and x_min. This is a generalization of the simple transformation y(t)=sgn[x(t)], for which a rigorous result was obtained recently. So far numerical experiments have shown that a power law spectrum 1/ƒ^α appears to be transformed again into a power law spectrum 1/ƒ^β under rather general condition for the truncation levels. We examine the above numerical results analytically. When 1<α<2 and x_max=-x_min=a, the transformed spectrum is shown to be characterized by a certain corner frequency ƒ_c which divides the spectrum into two parts with different exponents. We derive ƒ_c depending on a as ƒ_c ∼ a^-2/(α-1). It turns out that the output signal should deviate from the power law spectrum when the truncation is asymmetric. We present a numerical example such that 1/ƒ² noise converges to 1/ƒ noise by applying the transformation y(t)=sgn[x(t)] repeatedly.

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