We study nonlinear effects in step bunchingin a surface diffusion field with a directelectric current.Linear stability analysis showsthat the bunching instability occursin sublimation at long wavelength if the step distance is smaller than the surface diffusion lengthand the drift of adatoms induced by the electric currentis in the step down direction.When we take account of the nonlinear effect, the density of steps obeys the Benney equation, which shows an array of step bunches or spatiotemporal chaos.This feature is similar to the step bunching causedby the asymmetry of step kineticsexcept that the surface profile may change withthe sign of the dispersion term.

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A simple model of the persistent current in the presence of a many-bodyinteraction in a mesoscopic ring is presented.The Bethe ansatz approach is used to findexact solutions. Cases of both the absence and presence ofimpurities are solved and compared. It is indicated that neither impuritiesnor hard-core interaction affect the persistent currentexplicitly if there is a large number of electrons in the ring.

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Nonequilibrium transport properties are studied in an array of twoquantum dots connected in series, taking account of the long-range charging effect.The current and its fluctuation are calculated by solving theMaster equation.At low bias voltages, we propose two types of transport; one isa regular motion of charges, one by one, which corresponds to the minimum of the current fluctuation, and the other is an irregular motion, which corresponds to a local maximum. Their interplay results innew rich structures of the Coulomb blockade current oscillation, as a function of the gate voltage.With increasing bias voltage, the current fluctuation goes to aconstant level which is one third of the classical shot noise.

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The electrical resistance of solid oxygen is measured for the first time at room temperature under high pressures produced by a diamond anvil cell. The resistance becomes measurable at pressures above 65, GPa and decreases rapidly with increasing pressure, reaching around 3× 10^-1, Ω · cm at 95± 5, GPa.

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Superconductivity has been observed in single-crystalline Sr_1-xLa_xTiO₃samples for x = 0.001 and 0.009, which were previously classified as nonsuperconducting semiconductors. The relation between the critical temperature T_c and the carrier density n is comparable with those previously observed in Nb-doped or reduced SrTiO₃ systems. The apparent universality of the relation suggests that T_c in the doped SrTiO₃system is predominantly determined by n and independent of the method of doping.

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The asymptotic form of the normal-state c-axis resistivity ρ _c(T, H) was derived from the analysis of experimental data for Bi-2201 single crystals which have a T_c of 24--25, K in the ranges of temperature 5<T<120, K and magnetic field 0≤ H≤ 17T. The resistivity ρ _c(T, 0) without magnetic field is almost proportional to -log T with a small correction term and diverges as T→ 0. In contrast, the divergent profile of ρ _c(T, H) is suppressed in intense magnetic fields of H≥ H₀ where H₀ is about 9, T.

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We have measured the electrical resistivity and Hall resistivity in the flux flow state to investigate the superconducting mixed state properties in a CeRu₂ single crystal. We found that the peak effect, discussed in relation to the Fulde-Ferrel-Larkin-Ovchinnikov (FLLO) phases, persists up to a higher temperature than that reported previously based on magnetization and elastic measurements, which contradicts with the original FFLO theories. We have estimated the pinning force density from the dependence of the flux flow transport properties on the current density. We also report the normal state transport properties and the magnetization and compare them with those given in a recent report in which possible multiple phase superconductivity was proposed.

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We present a quasi-classical Green's function theory for the rough surface effects on d-wave BCS states.We reformulate and generalize the randomly rippled wall modelof rough surfaces so that it can describe the surface scatteringranging from the specular limit to the diffusive limit.We givea formal solution of the quasi-classical Green's function in a semi-infinite geometry with arbitrarily rough surfaces.The formal solution satisfies the boundary condition.We apply this method to the two-dimensional d^2-y2 and d_xy statesand show how the self-consistent order parameter and the surfacedensity of states change according to the surface roughness.The present analysis is relevant to tunneling spectroscopyof cuprate superconductors through the surfaces parallel tothe c-axis.

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We study an electron-phonon model with on-site Coulomb repulsionsU_ee at half filling by exact diagonalization combined witha mean-field approximation which gives accurate resultsin the narrow-bandwidth case.Superconductivity with off-site pairing is found to exist withan inverse isotope effect if and only if the phonon-mediatedattraction is almost offset by U_ee.

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Thermopower of a layered perovskite superconductor, Sr₂RuO₄, is studied. The magnitude of the thermopower in the conducting plane is about 29, μ V· K^-1 at 300, K. Above 4.2, K thermopower increases almost linearly with temperature, and it tends to saturate at high temperature. Thermopower is positive in the measured temperature range. The temperature derivative of thermopower shows a sharp change at about 20, K where no anomaly has been reported for other physical properties of Sr₂RuO₄.

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The thermal conductivity κ of sintered samples of YBa₂Cu₃O_y has been measured below 4.2, K. In the region of y≤ 6.4, phonon and magnon contributions to κ can be separated by considering the difference between their T-dependences. By considering the y-dependence of κ, we can also separate the electron thermal conductivity κ _el from κ, although it has been found to have the same T-dependence (κ _el∝ T²) as that of the phonon contribution κ _ph. This T-dependence is consistent with the d-wave symmetry of the superconducting order parameter. The magnon thermal conductivity κ _m exhibits a crossover of its T-dependence around the temperature characterized by the interbilayer exchange coupling between Cu spins, J_⊥. Information on the y-dependence of the superconducting order parameter has been deduced from that of κ _el.

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We have, for the first time, succeeded in preparing a single crystal of UNi₂Al₃ exhibiting both superconducting and antiferromagnetic ordered phase transitions. The magnetic susceptibility in the normal and paramagnetic state for the external magnetic field H applied parallel to the hexagonal a-axis, is found to be larger than that for the field applied along the c-axis. The upper critical magnetic field H_c2(T) for H // a-axis is much larger than that for H // c-axis. No flattening due to the Pauli limiting effect has been observed in the H_c2 vs. T curve. Comparison of these results with those of the isostructural compound UPd₂Al₃ suggests that the superconducting state is strongly related to the antiferromagnetic ordered state.

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We have studied the temperature dependence of the electrical resistivity, the magnetic susceptibility and the high-field magnetization of CeNi₂Ge₂. Quadratic temperature dependence of the resistivity is observed below 0.7K. The susceptibility exhibits a broad maximum at 28, K. Magnetization shows metamagnetic behavior at H_M-- 42, T as in CeRu₂Si₂. These results indicate that CeNi₂Ge₂ is a new heavy-fermion compound showing the metamagnetic behavior in the nonmagnetic ground state.

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We study ground state properties of the S=2 quantumantiferromagnetic chain with a bond alternationH = ∑_j [ 1 + δ (-1)^j ] S_j · S_j+1by a Quantum Monte Carlo calculation.We find that the hidden Z₂ × Z₂ symmetry is brokenfor 0.3 < |δ| < 0.5 while it is unbroken in the other regions.This confirms the successive dimerization transitions firstpredicted by Affleck and Haldane.Our result shows that these transitions can be understoodin terms of the hidden Z₂ × Z₂ symmetry breaking, as was discussed using the Valence-Bond-Solid states.Furthermore, we find that the behavior of the generalized string correlationis qualitatively very similar to that in the Valence-Bond-Solidstates, including the location of zeroes as a function of theangle parameter.

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We present a theoretical model for CaV₃O₇:the 1/4-depleted square spin-1/2 Heisenberg modelwhich includes both the nearest-neighbor coupling (J) and the next-nearest-neighbor coupling (J'), where J and J' are antiferromagnetic.Recent investigations on neutron diffraction by Harashina et al. revealed the occurrence of magnetic ordering at low temperatures, which may be called a stripe phase.It is shown that the observed spin structure is not stable according to the classical theory.By employing the modified spin wave theory, we show thatthe stripe phase is stabilized by the quantum fluctuationsfor J'/J > 0.69.In CaV₃O₇, J and J' are estimated to be nearly equalthroughout comparison of the theoretical and experimental results.

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The spin structure of magnetically ordered CaV_3O_7 has been determined by neutron powder diffraction.The structure is different from that expected within a simple classical Heisenberg model and therefore quantum effects seem to be significant in this system.By comparing the ordered moments of V⁴⁺ spins at two distinct sites with those derived using the modified spin wave theory [Kontani et al.: J. Phys. Soc. Jpn. 65 (1996) 1566.], information on the exchange coupling constants between V-spins can be obtained.

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In a single crystal of C₆₀, a decrease in conductance (negative photoconductance) with a response time of --0.01 s, followed by positive photoconductance with a longer response time, was observed upon irradiation with chopped light in a narrow energy region centered at 1.65 eV at room temperature. With decreasing temperature, the positive photoconductance is suppressed, but the negative photoconductance increases and has an increased response time. The dramatic relationship between the positive and negative photoconductances appears in a limited temperature range near that of the structural phase transition. The result can be interpreted by assuming the coexistence of traps with a slow thermal ejection rate and rapid recombination centers after Stöckmann.

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Optical absorption spectra have been measured for finite-chain analogs of linear polysilane, silicon oligomers CH_3[Si(CH_3)_2]_nCH_3, with controlled chain length n(=2 to 16).The intense lowest electronic absorption peak and its higher-lying side bands, which correspond to the one-dimensional exciton series in the infinite chain, shift to higher energy with decrease of the chain length because of the confinement of the excited states.The oscillator strength of the main absorption peak increases with the chain length, while the linewidth of the main peak drastically decreases, especially in the region n=2 to 6.These finite size effects of the electronic (excitonic) absorptionare argued in terms of spatial extension of the excited states, motional narrowing and electron correlation effect.

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We study a Brownian motion model of non-Hermitian matrix elements and show a mapping from random matrices to integrable quantum Hamiltonians of type V. This mapping has not yet been known and reveals a simple structure behind quantum Hamiltonians of type V.

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We have shown a unified technique how to derive exact solutions of the Toda equation written by the various special functions. The derivation method consists of the combinations of i) Hirota bilinear method of the soliton theory, ii) recurrence relations of the special functions and iii) elementary matrix calculations. The method is relatively easy and yet able to derive sufficiently wide class of special function solutions of the Toda equation.

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The Davey-Stewartson (DS) equations with a perturbation term are presented by taking a fluid system as an exampleon an uneven bottom. Stability of dromions, solutions of the DS equations with localized structures, against the perturbation is investigated numerically. Dromions decay exponentially under an effect of the perturbation, while they travel stably after the effect disappears. The decay ratio of dromions is found to have a relation to velocities of dromions. The important role played by the mean flow, which acts as an external force to the system, is discussed. These results show that dromions are quite stable as a localized structure in two dimensions, and they are expected to be observed in various physical systems such as fluid or plasma systems.

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We propose an efficient Monte Carlo algorithm for simulating a “hardly-relaxing” system, in which many replicas with different temperatures are simultaneously simulated and a virtual process exchanging configurations of these replicas is introduced. This exchange process is expected to let the system at low temperatures escape from a local minimum. By using this algorithm the three-dimensional ± J Ising spin glass model is studied.The ergodicity time in this method is found much smaller than that of the multi-canonical method.In particular the time correlation function almost follows an exponential decay whose relaxation time is comparable to the ergodicity time at low temperatures. It suggests that the system relaxes very rapidly through the exchange process even in the low temperature phase.

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We propose a new method for exact analytical calculation of the ground-state energy of the Ising spin glass on strips. An outstanding advantage of this method over the numerical transfer matrix technique is that the energy is obtained for complex values of the probability describing quenched randomness. We study the ± J and the site-random models using this method for strips of various sizes up to 5×∞. The ground-state energy of these models is found to have singular points in the complex-probability plane, reminiscent of Lee-Yang zeros in the complex-field plane for the Ising ferromagnet. The ± J Ising model has a series of singularities which may approach a limiting point around p -- 0.9 on the real axis in the limit of infinite width.

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We study fractional exclusion statistics for SU(2) symmetric quantum systems ofarbitrary spin S by generalizing the thermodynamic equations with squeezed strings proposed by Ha and Haldane.The bare hole distributions as well asthe statistical interaction defined by aninfinite-dimensional matrix specifythe universality class.It is shown that the system is described by the level-2S WZW model and has a close relationship to non-abelian fractional quantum Hall states. From a low-energy effective theory of our higher-spin model, the sector ofmassless Z_2S parafermionsis extracted, whose statistical interactionis given by a finite-dimensional matrix.

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We construct thermodynamics of the one-dimensional supersymmetric t-J model with the 1/sin^2 interaction and hopping. The thermodynamics is described exactly in terms of free spinons and holons obeying Haldane's fractional exclusion statistics at all temperatures. Moreover, at low temperatures the semionic spinons and holons decouple resulting in the spin-charge separation in thermodynamic properties.We obtain explicit results for the spin and charge susceptibilities and specific heat, and interpret them in terms of the fractional exclusion statistics. Extension to the multi-component t-J model shows that the excitations obey either fractional statistics for g-ons with partial polarization of components, or the parafermionic one without polarization.

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The dependence of the normalized mean multiplicity, R_A and reduced multiplicity R_S on the enrgy of the projectile in the energy range -- (2--200)A GeV, has been investigated. Furthermore, the dependence of R_A and R_S on the mass of the projectile and target nucleus in 4.5A GeV ¹²C-nucleus interactions have also been studied. The variations of R_A and R_S are found to increase linearly with increasing value of the multiplicity of charged secondaries produced in 4.5A GeV/c ¹²C-nucleus collisions. The results reveal that the normalised and reduced multiplicities of relativistic charged particles depend strongly on the projectile mass. The results reveal that the nature of the dependence of R_A on various parameters are identical with those obtained in high energy hadron-nucleus interactions. Finally, the values of the normalised moments of the multiplicity distributions of charged shower particles for different groups of emulsion nuclei were found to be nearly the same.

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We consider a system consisted of even valence-shell electrons according to the LCAO-ASMO-SCF theory, and we first point out that the extended INDO method proposed by Sugimoto et al. Can systematically be formulated by taking account of the zeroth- and first-order effects in respect to overlap integral S_μ(A)ν(B) between atomic orbitals (μ, ν) on bonded atoms (A, B) . On this basis, the approximate expression of ground-state configuration energy E_g is divided into several parts using π - and σ -type bond orders, and a general relation between bond length and bond order is derived by approximating S_μ(A)ν(B) and two-center Coulomb integral γ_s(A)s(B) (s denoting 1s- or 2s-orbital) as quadratic functions of bond length R_{[AB]} . Finally, the reasonability and usefulness of this relation are discussed in §5.

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Damping of quantum superposition of displaced states such as a Schrödinger cat state and a displaced thermal state interacting with a thermal reservoir is studied in a density operator formalism. The master equation approach is employed and the solution is shown to be factorized to a thermal density operator and displacement operators. This formalism is applied to the cat generating experiment proposed by Brune et al. [Phys. Rev. A 45 (1992) 5193], and the field evolution is obtained analytically.

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Linear stability of the square cell flow represented by the stream function:{Ψ} = sin x sin y is investigated numerically in various bounded region D = [0, M π] × [0, N π].The disturbances are limited to two-dimensional ones and a perfect slip condition is assumed to be applied.Special attention is paid to clarify how the critical long-wave mode (or large-scale mode) of the flow in unbounded region is modified by lateral boundaries.It is shown that the critical modes areclassified into three cases according to the configuration (M, N):(i) M=1, (ii) (M, N)=(2, odd numbers), (3, , 4) and (3, , 5), and (iii) the others. The last one is the most typical cases and is related to the long-wave mode in the unbounded region.The structure of the mode is one stationary vortex with the system size, which we call global rotation, for M -- N whileit is a series of stationary counter-rotating vortices for M << N.In case (ii) the critical modes are oscillatory though they are related to case (iii).In case (i) (linear array of vortices) the mode also shows the global rotation, but it is not related to the long-wave mode in the unbounded region.

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Dynamical behavior of a localized linear array of vortices is investigated by numerical simulations. The physical setup consists of a thin fluid layer (electrolyte) enclosed in a rectangular box and the vortices are locally driven by electromagnetic forces in the vicinity of a long lateral wall. The numerical model is used to simulate the Navier-Stokes equations in two dimensions with steady forcing and linear bottom friction. The model provides an accurate representation of the evolution of flow pattern: a stable unit-type flow with a group of four vortices and an irregular flow including large-scale motion. Fourier decomposition of the streamfunction shows that the mode of twice the wavelength of the forcing scale is prominent in the primary instability and a large-scale mode (uniform along the periodic direction) appears in the secondary instability. The mutual interaction between the unstable modes is shown to play an important role in dynamical behavior in the regime of transition to turbulence.

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The stability of the flow past a row of square bars, which is placed across a uniform flow, is investigated numerically. Two-dimensional and incompressible flow field is assumed. It is found that each jet which flows between the square bars is independent of each other when the pitch-to-diameter ratio of the row is large. However the confluence of several jets occurs when the pitch-to-diameter ratio is small. It is found that the confluence of couples or triplets of jets is a consequence of a pitchfork bifurcation and the critical Reynolds numbers for the pitchfork bifurcations are evaluated for each value of the pitch-to-diameter ratio. An experiment to visualize the flow field is also made and the confluence of jets is confirmed.

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The stability of the two-dimensional thermal convection in a square cavity heated from one side is investigated by restricting two-dimensional disturbances. The four sides of the cavity are assumed to be rigid and perfectly thermal conducting. The fluid is in a motionless state when the cavity is placed horizontally with the hotter side down. A thermal convection occurs as a pitchfork bifurcation from the motionless state due to the instability if the temperature difference exceeds a critical value in that case, but it always occurs even if the temperature difference is very small when the cavity is tilted and the bifurcation is the imperfect pitchfork bifurcation. The equilibrium state of the convection is calculated numerically in the range of 0°- 90°for the angle of the tilt. The stability of the equilibrium state is also investigated. It is shown that the instability occurs as a Hopf bifurcation or a pitchfork bifurcation depending on the angle of the tilt.

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Solid-solid phase transition of n-C₃₆H₇₄ was investigated by DSC and X-ray diffraction methods. In the original monoclinic single crystal, molecular chains inclined about 27° in the bc-plane from the normal to the lamellar surface. During the transition started from 72°C and completed at 73.4°C, two kinds of mechanisms were observed in the formation of a high temperature monoclinic structure having the molecules inclined about 19° in the ac-plane. One mechanism was due to formation of twinned crystals where the transition was developed on the frontier of the (110) twin boundary. The twin formation was achieved by rotation of the molecular zigzag plane producing the new crystalline a-axis deviated by 67° from the original orientation. The other mechanism was attained by changing the molecular staggering by 90° where the crystalline axis was unchanged. In the solid-solid transition, the two mechanisms appeared simultaneously, resulting in the appearance of polycrystals.

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Two-melt phase separation in the liquid Sn--SnSe system was investigated by measuring the velocity of sound. The newly determined phase boundary is characterized by the critical point at 865± 3°C at 33± 0.5, at.% Se and has a critical index close to 1/3. It is found that the velocity of sound in an alloy with a miscibility gap bends down as the phase boundary is approached from above, while it increases linearly with lowering temperature in an miscible alloy. The Fixman theory can satisfactorily explain the critical sound wave propagation.

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Neutron coherent scattering study at the structural phase transition point of KDCO₃ crystal has been carriedout. Strong quasielastic diffuse scattering is observed. From the detailed analysis of the intensity distribution in a wide range of the reciprocal space, we conclude as follows:(i) Even at T > T_c, the individual dimer is already deformed by the self-trapping of deuterons, thus locally breaking the symmetry of the averaged lattice within the time interval determined by the energy resolution limit of the spectrometer (τ<0.8×10^-11 sec).(ii) The inter-dimer interaction takes place via the strain field induced by the deformed dimers in the self-trapped state.(iii) The structural phase transition is triggered mainly by the strain-mediated indirect interaction between the dimers.

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The dynamical behavior of the order parameter at structural phase transitionin KDCO₃ is investigated theoretically.In particular, recent experimental results on ultra high energy resolution neutron spectroscopy using TASSE (triple axis spin echo spectroscopy) technique are analyzed and compared with the results of the ultrasonic measurements. It is verified that analysis based on generalized-Langvein equation of motion of pseudospin-phonon coupled system can give overall agreements with the results of both neutron scattering and ultrasonic measurements.

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The Mermin-Ho texture of a superfluid ³He A-phase confined in a rotating cylinder is studied.The case of a strong magnetic field applied along a cylinder axis is considered.The l and d textures are determined as a function of the angular velocity ω of the rotation.The lowest transverse NMR frequency of the spin wave mode is calculated from the obtained l and d configuration.In the rotating system, the energy term -ω L_z lifts the degeneracy of the two types of Mermin-Ho textures which have positive and negative superflow angular momentum L_z around the cylinder axis. These phenomena are expected to be identifiable by the NMR spectrum observation.

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The Al 2p photoemission spectrum has been measured at low temperature (35, K) with a resolution of 112, meV using synchrotron radiation. From the observed spectrum, the surface component lines were clearly resolved from the bulk. The spectral line shape has been analyzed by a least-squares-fitting method, and the precise values of the singularity index, the lifetime width and the spin-orbit splitting were obtained. We found that the singularity index is 0.058± 0.002 and is considerably smaller than those reported previously.

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The scaling property of level statistics in the quantum Hall regime, i.e. 2D disordered electron systems subject to strong magnetic fields, is analyzed numerically in the light of the random matrix theory. The energy dependences of the effective level repulsion parameter, the two level correlation, the GUE-GOE crossover parameter, and the rigidity (or {Δ}_3-statistics) of the level distributions are investigated for different system sizes by unfolding the original data and by dividing the unfolded spectrum into small regions. It is shown that the critical exponent of the localization length as a function of energy can be determined through the energy dependence of the level statistics. The analyses are carried out not only for the lowest Landau band (LB) but also for the second lowest LB. Furthermore the effect of finite range of disordered potential is studied. The short-ranged potential case in the second lowest LB is found to be pathological as in other studies of critical behavior, and it is confirmed that this pathological behavior is improved in the case of disordered potential with finite ranges.

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We have succeeded in oberving the de Haas-van Alphen (dHvA) effect in the mixed valent superconductor CeCo₂. The detected dHvA frequencies range from 6.24× 10⁵ Oe to 8.77× 10⁷ Oe. The largest frequency branch shows almost no angular dependence, indicating a nearly spherical Fermi surface. The cyclotron effective masses are found to be highly enhanced compared to the free-electron mass m_0, ranging from 0.97 m_0 to 10.9 m_0. The magnetoresistance measurements gives an evidence that the Fermi surface sheets are all closed without any open orbits. Band structure calculation based on a relativistic linear augmented-plane-wave (RLAPW) method, assuming the 4f electrons as itinerant, is in reasonably good agreement with the experimental dHvA results.

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The Hall-effect measurement technique is extended into multiply connected systems through a transport investigation of a double-boundary geometry fabricated on two-dimensional (2D) GaAs/AlGaAs heterostructures and three-dimensional (3D) GaAs epilayers. The study begins with the identification of a complement of the Hall bar (“anti Hall bar”) which may be utilized to generate a Hall effect within interior boundaries, when current is passed via interior contacts. Then, a double current technique is applied in the `anti Hall bar within a Hall bar' configuration in order to demonstrate current compensation in the magnetoresistive voltages, and the superposition properties of Hall's effect in 2D and 3D systems. The experiments show that (i) the Hall effect on a boundary depends exclusively on the current injected via the same boundary, while (ii) the magnetoresistive voltages are insensitive to the origin of the current within the specimen. The invariance of these features from the classical- to the quantum--limits suggest that the bulk current is maintained under steady-state quantized Hall effect (QHE) conditions, while the observation of dual simultaneous quantum Hall plateaus provides a new perspective into aspects of the `gauge argument' thought experiment (R. B. Laughlin: Phys. Rev. B 23, 5632 (1981)), by revealing some peculiar changes in the Hall measurement upon the application of `periodic boundary conditions' in 2D cylinder type geometries.

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The localization length ξ for four kinds of the 1D random potentials (a δ-function type and three Kronig-Penny types) has been calculated numerically as a function of the electron energy and two parameters specifying the randomness of the potential (the maximum strength of the potential and the average interval a between neighbouring impurities). A length parameter s is introduced which is related to the fluctuation of the potential. We have found that ξ/s depends only on ks for ka<1, where k is the electron wave number. The function relating ξ/s to ks is found to be universal for the four kinds of the potential considered here.

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The electrical resistivity in organic superconductors show the T^2-dependence at low temperatures above T_c. This fact suggests that the electron-electron interaction determines the damping of quasi-particle in the Fermi liquid state. In this paper, we calculate selfconsistently the temperature dependence of damping rate due to the electron-electron interaction. Then, using this damping rate, we calculate the temperature dependence of NMR relaxation rate, for the two cases with s and d-pairing states, respectively. Our result shows that, when the damping rate at T_c is of the same order as T_c, no coherence peak appears in T^-1_1 even if the superconducting state possesses s-wave symmetry. However, we cannot eliminate a hump structure appearing at low temperatures, at which the s-wave gap begins to open against the damping effect. On the other hand, the relaxation rate for d-wave decreases smoothly. This is the important difference in determining the pairing symmetry. We discuss the comparison of our result with experimental data for several systems.

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It is demonstrated that a k-dependence of the hybridizationmatrix element between f- and conduction electrons can give rise toan anisotropic hybridization gap of heavy fermions if the filling ofelectrons corresponds to that of the band insulator. The most interestingcase occurs when the hybridization vanishes along some symmetry axisof the crystal reflecting a particular symmetry of the crystal field.The results of a model calculation are consistent with wide range ofanomalous properties observed in CeNiSn and its isostructural compounds, the anisotropic semiconductor of heavy fermions. In particular, highlysensitive effect of impurity scattering on the residual density ofstates for zero energy excitation and the anisotropic temperaturedependence of the resistivity are well explained. It is also discussedthat a weak semimetallic behavior arises through the weak k-dependence\of the f-electron self-energy Σ_f(k, 0).

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By means of neutron powder diffraction on antiferromagnetic samples of BaCo_1-xNi_xS₂, the spin structure has been determined.The magnitudes of the ordered moments are -- 2.9μ_B at 10 K for x=0.0 and -- 1.7μ_B at 100 K for x=0.175.The results are not compatible with the electronic configuration (3d_{3z²-r²})^1+x, which was previously assumed to explain the physical behavior of the system.Instead, the configuration seems to be (3d_yz or 3d_zx)¹ (3d_{3z²-r²})¹ (3d_{x²-y²})¹ in BaCoS₂.Each Ni atom substituted for Co adds one electron to this system.Based on this basic picture of the electronic structure, various physical properties of BaCo_1-xNi_xS₂ ever published are discussed.

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The magnetic phase diagram of β -Mn(Sn) alloy was determined by Mössbauer spectroscopy. Even the 0.1 at.% Sn alloy shows magnetic freezing below a transition temperature. The magnetic transition temperatures are nearly proportional to the square roots of the Sn concentration. No qualitative difference in the hyperfine field distribution function is found between the 0.1 and the 7.0 at.% Sn alloys.

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The ground state and collective modes of spin density wave (SDW) states with a quarter-filled band are examined in the presence of a two-fold periodic potential which originates in the anion lattice of organic conductors. The competition between the potential, W_0, and the commensurability energy results in the coexistence of the 2k_F-SDW and the 4k_F-CDW (charge density wave) and the reduction of an excitation gap for the longitudinal mode. The W_0-dependence of the gap is examined in terms of a phase Hamiltonian.

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Electron Spin Resonance (ESR) measurements have been performed on axial triangular antiferromagnets CsNiBr_3 and CsMnI_3 in their lowest three-dimensional (3 D)ordered phase. The frequency vs. magnetic field diagrams are obtained in the frequency range from 9 to 380 GHz and the magnetic field up to 160 kOe. Several significant disagreements between the experimental data and the theory based on the conventional model are found. It is shown that the disagreements can be removed by the diagonal interchain exchange coupling J_2. The ESR theory is developed taking the J_2 coupling into account. Fitting the present theory to experimental data, the interaction parameters of CsNiBr_3 and CsMnI_3 are determined.

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Growth kinetics of domain structures in an incommensurate phase under an applied field is studied by solving the kinetic equation numerically. A two-dimensional model, applicable to the crystals such as NaNO₂ and SC(NH₂)₂, is adopted. In a weak electric field the amplitude of the incommensurate modulation increases at first and then the annihilation of phase defects proceeds as time goes on. On the other hand, in a strong electric field the appearance of the incommensurate structure is entirely suppressed and the ferroelectric state is established immediately after quenching. In an intermediate strength of the electric field the nucleation of the incommensurate phase takes place at various positions and then their growth follows with a constant velocity.

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We study the intraband energy-relaxation of excitons localized at a stacking fault interface in a layered crystal BiI₃ observing the temporal behavior of the luminescence. The relaxation processes in this system are investigated by analyzing the time-resolved luminescence of a phonon sideband which directly reflects the exciton distribution in the band. When the exciton is resonantly excited by a picosecond laser pulse, the exciton population reveals a `hot' distribution at an early stage. The effective temperature decreases immediately according to the intraband energy-relaxation via the interaction with phonons, and after --40 psec, the distribution almost reaches the thermal equilibrium with the lattice. We obtain the consistent population relaxation time (T_1) from the three-beam degenerate four-wave mixing signals.

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