Level energies and γ-transition properties in the low-lying states of ¹²³Ba have been investigated through the decay of ¹²³La. From γ-ray singles and γ-γ coincidence measurements of the ¹²³La produced in the ³⁵Cl+⁹²Mo reaction and an on-line mass-separation technique, 12 new levels haye been assigned in the level scheme of ¹²³Ba. The [411]1/2⁺ band, consisting of 6 members, has been proposed.

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It is shown that discrete sine-Gordon systems form a number of types of hierarchical discommensuration patterns simultaneously, with much different scales and different dimensions, which is the extension of one (type of) hierarchical discommensuration pattern with the system dimension which has already been shown. It is mathematically described by inverse matrix expansions and orthogonal transformations of the matrices which represent the structures of the system.

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The concept of sublattice strain is for the first time introduced using a simple two-sublattice model. Ferridistortive crystals are defined as crystals whose spontaneous strains consist of two kinds of sublattice strains with opposite signs and different magnitudes. Ferrielastics are defined as ferridistortive crystals in which the sign of one of the sublattice strains can be reversed by external stresses, and a triple hysteresis loop can be observed in a stress-strain curve, just as in the case of ferrielectric crystal a triple hysteresis loop is observed in an electric field-polarization curve. It is suggested by using the two-sublattice model that ferrielastics are in fact possible under certain conditions.

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Measurements of the dielectric constant, the DTA signal and the linear thermal expansion, optical observation of domain structure and X-ray examination of (CH₃NH₃)₄InBr₇ have been carried out over a temperature range from 25°C to 180°C. It is found that the crystal undergoes phase transitions at 171°C (T₁) and 141°C (T₂), and is ferroelastic below T₁. The crystal at room temperature belongs to monoclinic P2/n with lattice parameters: a=16.854(6) Å, b=7.731(6) Å, c=16.756(9) Å and β=103.22(2)°. When the symmetry is approximated as to be pseudo-orthorhombic by taking a′=a+c, b′=b and c′=c−a (β′=90.34(11)°), the domain structure observed below T₁ is deduced from the strain-compatibility relations for the domain boundaries by taking account of the symmetry change from mmm to 2/m at T₁. At T₂ no change of domain configuration has been detected.

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The relaxation process of the crystal shape near the facet is studied. We adopt a dynamical equation which takes account of the nonanalytic behavior of the vicinal-surface free energy to analyze the relaxation process of the crystal shape near the facet. During the relaxation process, the surface gradient p shows the Gruber-Mullins-Pokrovsky-Talapov behavior p∼(Δr)^1⁄2 (Δr: distance from the facet edge) off the facet edge. Quite near the facet edge, however, we obtain the ‘classical’ behavior p∼Δr. This result, dynamical transmutation of critical behavior, gives a possible explanation for the discrepancy between theory and experiment on the facet edge critical behavior.

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Quantum Monte Carlo study of the Hubbard model on a square lattice in the ground state is reported. For the on-site interaction U=4 scaled by the transfer, the charge excitation gap at the half-filling is estimated to be Δ_c=0.58±0.08. Near half-filling, the charge compressibility κ follows the form κ∝δ⁻¹ for the doping concentration δ, indicating a divergent behavior as the system approaches half-filling, while κ=0 at the half-filling. The incommensurate spin correlation length ξ scales as ξ∝1⁄\sqrtδ.

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The temperature dependence of the lattice parameters of the title compound has been determined by low-temperature X-ray diffraction measurements down to 20 K. It is found that the parameter a takes a minimum around 150 K and a maximum at 80–90 K, while other parameters of b and c, and the unit cell volume abc almost monotonically decrease with decreasing temperature. This anomalous change in the in-plane parameter a contrasts that in the interlayer spacing observed in κ-(BEDT–TTF)₂Cu(NCS)₂, but both structural anomalies correlate phenomenologically with the puzzling resistance maximum around 100 K observed to be common to these organic, high-T_c superconductors.

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It is shown that the method proposed by Nakajima to describe the spinon and holon degrees of freedom in strongly correlated electron systems is obtained as a special case of the quantized Bogoliubov transformation developed for a description of the nuclear pairing field.

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The S=1 antiferromagnetic Heisenberg chain in a magnetic field along the z-axis at T=0 is studied by numerical diagonalizations up to N=16 and an analysis of size corrections. We check that the system obeys the conformal field theory with the central charge c=1 in a magnetic state (0<m<1). We investigate the asymptotic form of the transverse and parallel spin correlations and give the exponents η and η^z, defined by ⟨S₀^xS_r^x⟩\simeq(−1)^rr^−η and ⟨S₀^zS_r^z⟩−m²\simeqcos (2k_Fr)r^−ηz. We determine η=1⁄2 and η^z=2 at m=0 and 1. In addition, we check the relation ηη^z=1, which is consistent with the Luttinger liquid concept. In terms of the concept, the anomalies of magnetization at m=0 and 1 are discussed.

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The ⁵¹V Knight shift and the quadrupole interaction in a triangular lattice compound LiVO₂ have been studied by means of the pulsed-NMR technique below the transition temperature T_t of about 450 K. From the analysis of the NMR spectrum, we determined the principal values of the electric field gradient (EFG) tensor and the Knight shift components along the principal axes of the EFG tensor. The Knight shift was found to be temperature independent, and its anisotropy could be attributed to the anisotropy of the Van Vleck orbital susceptibility. Spin contribution to the susceptibility is largely reduced below T_t, indicating a nonmagnetic spin-singlet state probably due to the clustering of V³⁺ ions.

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Dielectric anomalies have been recognized in temperature dependences of the dark dielectric response κ(T) and also the transient photoconductivity Q(T, λ) of insulating crystals of cuprous oxide Cu₂O. Unlike submerging characters of normal photoconductivity in most insulators, Cu₂O exhibits a series of step-like emergences of Q(T) with decreasing T in correspondence with the dielectric anomalies in κ(T) characteristic to electronic phase transitions. Anomalies in κ(T) and the step temperatures T_pS in Q(T, λ) of Cu₂O are, via the Y–Cu–O, La–Cu–O, correlated with the critical temperatures T_sC of superconductivity in ρ(T) of the Cu-based oxides such as the Y–Ba–Cu–O, La–Ba–Cu–O systems. Thus, Cu₂O can be considered to be the “basic host insulator” relevant to the Cu-based superconductors. Therefore, we can call such an anomalous photoconductivity Q(T) discovered in Cu₂O, Y–Cu–O, La–Cu–O as well over all host insulators of the Cu-based superconductors to be “Superconductive-Conjugate Photoconductivity”.

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Nonlinear optical phenomena have been observed for the first time in a new cyclotron resonance experiment on the photoexcited positive holes and/or electrons in Cu₂O at f=35 GHz, T=4.2 K and at high density excitation P_ex≥100 kW/cm² of λ_ex=460–750 nm. Unexpectedly, we have observed a nonlinear optical growth of the cyclotron resonance absorption of both holes and electrons at the mid-gap high-density excitation of λ_ex≥690 nm. New experimental results reveal so far unknown specific characters of the conduction and valence electrons in detail and of deep levels as well. Here, we tentatively ascribe these phenomena to a possible condensation of polarons and excitons into a new state in Cu₂O such as into a bipolaron state via a specific type of double acceptor states.

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Details of the temperature dependences of transient photoconductivity Q(T, λ) with that of Hall mobility μ_H(T) of photoexcited carriers in Cu₂O at low power level of λ_ex=570–735 nm have been reexamined over a wide temperature range between 4.2 and 300 K in order to clarify the natures of “supercondcutive-conjugate photoconductivity”. Selective optical excitation at low levels of λ_ex=570–750 nm creates either a free electron and a positive hole or mainly free holes in Cu₂O. By carefully analyzing these data, we have recognized for the first time a novel quantized series of “Step Temperatures T_pS” in Q(T, λ) with “Clew Temperatures T_pC”, in the photoexcited holes density n_p(T, λ) in Cu₂O as T decreases. A series of the values of T_pS or T_pC is possibly ruled by a type of condensation of valence electrons and free photocarriers into new states mediated via surrounding intraband CT-excitons of Cu₂O. Here, we propose a new concept of “the excitonic isomer shift of superconductive T_sC”.

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The methodology of Riemann-Hilbert transform is adopted to obtain exact solution of the deformed NLS equation;
(Remark: Graphics omitted.)
deduced by Burtsev et al. It is observed that the required analytic structure is determined by the “constant” part of the otherwise space-time dependent spectral parameter λ(x, t). Lastly a direct substitution verifies the solution.

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When a quantum wire is not straight, an effective potential appears in the Schrodinger equation according to its curvature. Generally due to this geometrical potential the electron along the wire cannot change its direction of the motion without reflection. Here, the new curve is proposed in which the electron traverses changing its direction without reflection. The curve is determined under the condition that the effective potential should be reflectionless one which is well-known in the scattered problem.

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Propagation of solitons in nonuniform media is examined by the K-dV equation with sinusoidal nonuniformity and dissipation terms. Under a certain balanced state between these two terms, it is observed numerically, for two different types of dissipation, that the soliton is trapped on some phase point of the medium and behaves like a localized pulse. This trapping can be explained fairly well by the soliton-perturbation approach when the nonuniformity is moderate and the dissipation is weak.

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A motion of a Gaussian wave packet of a single electron in a harmonic potential is obtained by solving the time dependent Schrodinger equation analytically. The analytic formula of the phase of the wave function which depends on both time and space is also presented explicitly. The probability density of the wave packet moves changing its width and central position periodically. The period of the change of the width is half of that of the central position. The interpretation of these periodic changes in terms of the Green’s function which can be derived by the path integration formulation is also discussed.

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The dual transformation is applied to the (1+1)-dimensional O(3) nonlinear sigma model where the field variables are defined on the two-dimensional unit sphere with the metric G_μν. We show that the dual transformation yields a new system with the metric G_μν⁻¹. We also show that the topology of the ‘dual surface’ is different from the original sphere.

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Quantum simulation algorithm for the lattice fermions in the ground state is examined. Initial trial state is optimized using the unrestricted Hartree Fock solution. Convergence to the ground state average in the projection process is compared among several choices of the trial state. The optimized trial state provides a faster convergence for physical quantities as well as a better minus sign ratio in the sampling.

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Binary encounter electrons originating from collisions between 56 MeV Si^q+ and He have been measured at zero degrees with respect to the beam direction. The dependence of the binary-encounter peak on the projectile charge state q=6, 12, 13 and 14 (fully stripped Si) was studied. As earlier observed by Richard et al. (J. Phys. B 23 (1990) L213) using fluorine ions, we found that the binary-encounter electron production increased for decreasing charge state. This dependence which reflects the importance of outer screening has recently been treated in several theoretical papers and the present results are compared to estimates by K. Taulbjerg (private communication).

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Slow translation of a thin circular annulus in an unbounded viscous fluid is investigated on the basis of the Stokes approximation. Using a general solution for the Stokes flow, the problem is reduced to that of finding harmonic functions which satisfy three-part mixed boundary conditions. The formal expression for the flow is obtained by solving a set of triple integral equations. The solution is found after reducing the triple integral equations to integral equations which are amenable to treatment by well-tried numerical procedures. The drag exerted on the annulus is determined for various ratios of the inner to outer radius. Asymptotic expressions for the drag are obtained for a slender annulus.

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Wave propagation in weakly inhomogenious media is discussed. An approximate equation of shallow water waves propagating on a layer with both weakly and gently uneven bottom is derived from an exact system of equations. This type of equation has previously obtained by the present author for a rather wide class of systems. Based on the approximate equation thus derived, the effect of randomness on the propagation of the Burgers shock wave is studied.

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The radial electric field structure in helical system is discussed taking into account the effects of the orbit loss and charge exchange loss in addition to the neoclassical fluxes. Analysis is made for the CHS torsatron/heliotron, in which the radial electric field E_r was estimated experimentally. It was found that the fast ion orbit loss and charge exchange loss have strong influence on the profile of the radial electric field, particularly near the plasma periphery. The absolute value of E_r in the experiments is still more negative than the theoretical prediction.

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Temporal and spatial evolutions of plasma potential formation are experimentally investigated in an ECR plasma terminated by biased segmented endplates under a mirror configuration of magnetic field. The time scale of the potential formation is determined by ion transport perpendicular to the magnetic field. Nonaxisymmetric potential profiles formed by the biased segmented endplates are also observed to depend on the cross-field ion motion.

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The local electrostatic persistence length of wormlike polyelectrolyte chains in salt-free solutions is calculated, considering the strong electrostatic repulsion of chain segments. The chain conformation is assumed to be wormlike only locally, and the assumption on the radial distribution function g₂(R) of monomers in different polymers
−(n⁄N)∫(g₂(R)−1)dR=1
identical to that in the previous papers is also used, where n and N are the number concentration of the monomers and their total number in one polymer, respectively. The same results as the previous ones, that the persistence length is proportional to n^−1⁄2 in very large n and to (n⁄N)^−1⁄3 in very small n, are obtained. By adding to this result a term on the intrinsic chain stiffness, another equation of this length is obtained. These calculated results agree with experimental ones.

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The structural and dynamical properties of molten AgI are investigated using molecular dynamics calculations and pair potentials originally given by Parrinello et al. and modified by authors. The total pair distribution functions, thus obtained, are in good agreement with experimental results by Takahashi et al. and with theoretical results by Stafford and Silbert. The wave-number-dependent static dielectric function ε(k) is also calculated with use of the charge correlation function in the both α- and molten phases. In the α-phase, ε(k) is negative for small wave numbers and approaches zero at special wave numbers, which correspond to the positions of the Debye lines in the reciprocal lattice space. ε(k) in the molten phase shows the forerunning phenomenon to the crystalization, which is a very similar behavior to that in the strongly coupled one component plasma.

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The ultrasonic velocity in the α-quenched phase of Ag₃SI has been measured for the longitudinal wave at 10 MHz over the range from 80 K to room temperature with a pulse echo overlap method. Comparison is made with the results of the previous ultrasonic attenuation measurements. The change in the ultrasonic velocity with temperature is found to be due to the relaxation phenomenon of a thermally activated process and an anharmonicity of the lattice vibration. The electrical impedance has also been measured at frequencies between 10 kHz and 10 MHz over the same temperature range. Anomalous behavior is seen both in the electrical and ultrasonic measurements below about 150 K. The activation energy is estimated for the diffusive motion of Ag⁺ ions and a close agreement between the values deduced from two different experiments is obtained.

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An ionic plasma model is presented to describe the low-energy excitation of cation superionic conductors. When taking account of an effective charge of cations, the model is supported by experiments except for β-Alumina type superionic conductors.

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A computer simulation by a constant-temperature and constant-pressure molecular dynamics method has been applied to Ag₂Se to investigate the low temperature phase transition between a superionic phase and a nonsuperionic phase. The pair-wise potential model used by Rino et al. to study the superionic and molten state of Ag₂Se has been used. The low temperature structure obtained by the calculations is orthorhombic with a=4.29, b=6.82, c=8.25 Å, and the space group is Pmnb. This is very similar to that observed experimentally, which is orthorhombic with a=4.333, b=7.062, c=7.764 Å, and the space group, P2₁2₁2₁.

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We investigate the dynamical properties of the one-dimensional Hubbard model using the quantum Monte Carlo method and the numerical analytic continuation method based on the maximum entropy principle. Results for the spin, charge and current excitation spectrum are presented for various values of the coupling and the band filling for the system of 24 sites with the periodic boundary condition. We find that the total spectral density of the spin excitation exhibits a gapless structure irrespective of the coupling or the band filling. The charge excitation spectrum, on the other hand, clearly shows the gap formation at the half filled band and shifts its weight toward the higher energy region with increase of the coupling. This charge excitation gap, however, disappears with the hole doping. We also discuss the momentum dependence of the spectral functions.

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A study is given of the eifect due to the impurity correlation on Auger processes in a slightly compensated heavily doped semiconductor that is obtained by thermal preparation. Account is taken of high-temperature ionic correlation and low temperature electronic screening as well. Contrary to the case of close compensation, the impurity correlation in the sample in question is generally found to be of far less importance, reducing the Auger recombination only by about an order of magnitude in favour cases.

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Preparation of high quality conducting poly(cis-1,2-di(2-thienyl)ethylene), cis-PTE from the electrochemical polymerization of cis-1,2-di(2-thienyl)ethylene was tried. However, synthesized polymer was not cis-PTE but trans-PTE. The electrochemical, optical, and magnetic properties in the trans-PTE in comparison with those of polythiophene, PT, during electrochemical p-type doping have been investigated. These results are discussed in terms of polaron and/or bipolaron models. The band gap of trans-PTE was evaluated to be about 2.1 eV and almost the same as that of PT. The polaron states in trans-PTE appear in the band gap: ca. 0.5 eV above the valence band but ca. 0.8 eV below the conduction band. This result satisfactorily explains the stability of p-type doped trans-PTE compared with that of PT. Since the energy level of the bottom of conduction band in trans-PTE is higher than that in PT by ca. 0.2 eV, and successful n-type doping in trans-PTE is not expected.

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The temperature and magnetic field dependence of the electrical resistivity of black phosphorus single crystals prepared by the bismuth-flux method was measured down to 0.5 K in temperature and up to 6 T in magnetic field. While a typical semiconducting behavior of p-type conduction has been observed above about 10 K, the log T-like dependence of the conductivity and the log B dependence of the negative magnetoresistance have been found below 10 K. Results of the field dependence of the magnetoresistance are in good agreement with the theory of the two-dimensional Anderson localization. The whole results are understood by a model that the 3D hole conduction process in the high temperature region is replaced at about 10 K by a 2D electron gas confined near the surface.

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Magnetotransport studies of GaAs/Al_xGa_1−xAs superlattice having a tailored Fermi surface of a weakly corrugated cylindrical shape have revealed an angular dependent mangetoresistance oscillation effect similar to the one recently found in quasi-two-dimensional organic conductors. The present observation provides an evidence that the effect should commonly occur in a general class of nearly two-dimensional electron systems. Transport behavior has been studied both in the vertical and lateral direction of the superlattice, and is discussed in the light of our semiclassical calculation recently reported.

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The effects of pressure on the resistivity ρ and the Néel temperature T_N of UNiSn, UPdIn and UPdSn have been investigated up to 25 kbar. With the applied pressure, semiconducting behavior in UNiSn is suppressed and the presence of the Kondo like effect is revealed in UPdSn. Positive dT_N⁄dP of the ternary UTX is compared with that of binary U compounds and discussed in terms of the interatomic spacing of U atoms.

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Hall coefficient and electrical resistivity were measured on amorphous SnTe films by a high input-impedance technique. All the holes responsible for the metallic conduction in the crystalline phase are found to be localized in the amorphous phase, where the valence band mobility edge E_v lies about 0.11 eV below the Fermi level. The mobility gap was estimated to be about 0.58 eV. The Hall mobility of the nonlocalized holes near E_v is about four orders of magnitude smaller than that in the crystalline phase, suggesting a strongly disordered nature of the amorphous phase.

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The excess conductivity Δσ above the superconducting transition temperature was measured for the deposited layer of Pb fine particles prepared by the gas evaporation method. For the layer with larger particle size than the coherence length ξ(0) for pure lead, the temperature dependence of Δσ agrees with that of the fluctuation conductivity Δσ_3D for 3 dimensional system of the Aslamazov-Larkin theory, but for the layer with smaller particle size than ξ(0), Δσ deviates from Δσ_3D. It is considered that the deviation is due to the fluctuations arising across the many fine particles in the layer.

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We examined the two-dimensional antiferromagnetic Heisenberg model on frustrated lattices with arbitrary strengths of next-nearest-neighbor interaction by numerical diagonalization. We in particular calculated low excitation energies with total spin S=1 to 3 for various sizes N of lattices by using the free boundary condition. The excitation energies follow a finite size scaling for spin waves in the case of the free boundary condition and seem to vanish in the large-N limit. This result suggests that the ground state has a magnetic order and the excitations are spin waves for any strength of frustration.

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The impurity susceptibility of Mn²⁺ in antiferromagnetic CoCl₂2H₂O single crystal has been investigated using the ac-susceptibility method. Experimental results indicate that Mn²⁺ impurity spin couples weakly with host Co²⁺ spins and behaves as a localized paramagnetic spin in accord with the ESR results with the single ion anisotropy constant D of −0.13 cm⁻¹ and local effective field H_E of 36.7 kOe.

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Thermal expansion measurement has been carried out on single crystalline CeCu₂ and YCu₂ in the temperature range from 1.8 K to 300 K. The thermal expansions of CeCu₂ are highly anisotropic among each crystal axis reflecting orthorhombic crystal structure. A well-defined anomaly due to antiferromagnetic ordering is observed near 3.5 K in the temperature dependence of the linear thermal expansion coefficient α_i (i=a-, b- and c-axis). A magnetic contribution to α_i(T) due to 4f electron is estimated by comparing the α_i-T curve of CeCu₂ with that of YCu₂. We also discuss the magnetic contribution to volume thermal expanslon α_V(T) curve and attempt to analyze it on the basis of phenomenological theory.

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X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, and magnetic susceptibility measurements have been performed in the temperature range 4.2–293 K on the Al₇₀Fe₂₀Ta₁₀ icosahedral alloy. It was found that Fe atoms are distributed among a multiplicity of sites, which was interpreted as evidence of intrinsic disorder characteristic for icosahedral alloys. It was shown that the distribution of electric quadrupole interactions is better described by the Gaussian shape than by the shape predicted by the shell model. It was found that Al₇₀Fe₂₀Ta₁₀ is not magnetically ordered. We find that Al₇₀Fe₂₀Ta₁₀ is a paramagnet and that the claim made in the literature of the simultaneous occurrence of Curie-like and Pauli paramagnetism is an artifact resulting from previously unconsidered second phases.

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The absence of the Hebel-Slichter peak in the observed temperature dependence of the nuclear spin relaxation rate, 1⁄T₁, is investigated by evaluating the effect of fluctuations in the superconducting order parameter on the local electronic susceptibility. The interactions between fluctuations have been taken into account in order to smear out the peak in the immediate vicinity of the critical temperature T_c. It is found that, below T_c, 1⁄T₁ rapidly decreases in agreement with the experimental data.

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Magnetic properties of superconducting and nonsuperconducting Nd_2−xCe_xCuO_4−y are studied by observing EPR signal of doped Gd³⁺ ions which are embedded in Nd-magnetic lattice. Gd³⁺-EPR linewidth changes drastically below about 80 K in the compound with x=0. This change decreases with increase of Ce-concentration and disappears in the superconducting compounds. The drastic change of the EPR linewidth corresponds to Cu²⁺ spin reorientation detected by neutron scattering experiments. These results indicate that Ce-doping and furthermore, oxygen reduction lead to disappearance of magnetic moment on Cu ions and in such substances superconductivity is observed. On the other hand, with increasing Ce-concentration, the resonance field increases while the linewidth decreases. This result is discussed on the basis of variation of dipolar and exchange fields.

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Molecular motions and phase transitions in tris(methylammonium) nonabromodibismuthate (III), (CH₃NH₃)₃Bi₂Br₉, were investigated by measuring the temperature dependences of static and rotating frame ¹H spin-lattice relaxation times (T₁ ans T_1ρ) and the second moment (M₂) of ¹H NMR absorptions. Near 80 K in the lowest-temperature phase IV, the orientation of the methylammonium cation is almost fixed but the cation itself is rapidly rotating about the C–N bond axis. On heating, gradual disordering of the cationic orientations takes place in phases IV and III for two thirds of crystallographically nonequivalent cations and in phase II for the remaining cations. Finally, all the cations become to be dynamically disordered and undergo rapid overall reorientations in the room-temperature phase I. The IV–III transition at 108 K may be connected to dynamics of the inorganic (Bi₂Br₉³⁻)_n subsystem rather than the ionic motions. An anomalous behavior of ¹H T_1ρ, attributable to cross relaxation between ¹H and Br nuclei, was observed.

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NMR measurements were made for YCo₁₂B₆ and LaCo₁₂B₆ mainly by the steady-state method in zero external field as a function of temperature. Two ⁵⁹Co domain signals with quadrupole splittings and two wall signals with single lines were observed. With decreasing temperature, a low-frequency domain signal in LaCo₁₂B₆ vanished below about 25 K but another domain signal emerged below about 40 K, revealing a discontinuous change in frequency and in spacing between the quadrupole-split components. The specific heat of LaCo₁₂B₆ did not show any anomaly in this temperature range. These suggest that the observed change in NMR in LaCo₁₂B₆ around 35 K is not of first order but is presumably associated with a change in magnetic states. In YCo₁₂B₆ there was no such a discontinuous change in the NMR spectrum.

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Polarized reflectance spectra of a single crystal of κ-(BEDT–TTF)₂I₃ were measured at 295 K and 15 K over the spectral range from 500 cm⁻¹ to 25000 cm⁻¹. The infrared property was two-dimensional. Non-Drude mid-infrared features were observed in spite of the metallic dc conductivity. A comparison with β- and θ-(BEDT–TTF)₂I₃ shows that this behavior has a close connection with the dimeric structure of κ-salts. We analyzed the observed line shape by the curve-fitting analysis, and obtained optical effective masses. On the basis of the perturbation theory, an effective tight-binding band model for κ-salt was derived. We estimated the transfer integrals using this model.

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Excitonic properties of PbI_2(1−x)Br_2x mixed crystals have been investigated with attention to both the changes of the exciton-phonon coupling strength and of the magnitude of the alloy potential fluctuation. Below x=0.2, the exciton-phonon coupling strength becomes larger as x increases and a new broad luminescence band due to a self-trapped exciton state appears above x≈0.15. Physical parameters such as the excitation energy of the exciton and the exciton-phonon coupling strength change linearly with x following to the virtual crystal model. Above x=0.5, new reflectivity peak and luminescence band corresponding to the “orthorhombic PbI₂” are observed in stead of those of the hexagonal PbI₂. We also observe the luminescence from PbI₂-clusters because of the large potential fluctuation effect.

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Angle-resolved inverse photoemission spectra have been measured at room temperature on the layered transition metal dichalcogenides, 1T-VSe₂, 1T-TiS₂, 1T-TaS₂, 2H-NbSe₂ and 2H-TaSe₂, in the isochromat mode with a detection photon energy of 9.4 eV. Their energy dispersion curves are obtained along symmetry directions in the Brillouin zone and compared with theoretical band calculations.

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Soft X-ray emission spectroscopy due to the Cu 3d→2p electronic transition (Cu 2p-XES) is one of the powerful tools for investigating the local nature of the Cu 3d state in high-T_c superconductors. We theoretically investigate Cu 2p-XES for CuO and La₂CuO₄ based upon the impurity Anderson model and the formula of the second order optical process. Justification for this model is given by that available experimental data of Cu 2p-XES, 2p-XPS, 2p-XAS and 3d-XPS are satisfactorily reproduced in a unified way. According to Cu 2p-XES experiments so far made, a shoulder structure appears on the high energy side of the main peak in La₂CuO₄ and also in high-T_c superconductors, but it is absent in CuO. It is shown that the appearance of the shoulder structure originates from the stronger hybridization for the a_1g symmetry states in La₂CuO₄ than in CuO due to the existence of the apical oxygen.

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In this work we discuss the high-energy electron energy loss spectra from a deep core orbital in a solid based on many-body electron scattering theory developed by Fujikawa and Hedin. Important many-body effects are absorbed into damped one-electron functions and optical potentials. Particular emphasis is placed on the extended electron-energy-loss fine structures (EXELFS) or extended energy-loss fine structures (EELFS), where we have to prepare three different kinds of damping functions and the optical potentials. The first is for the incident fast electron, the second for the scattered electron after the loss, and the third for the secondary excited one from a deep core which behaves like an EXAFS electron. The second optical potential is related to the third one if we use quasi-boson approximation for the valence electrons. Furthermore we explicitly include elastic scatterings of both probe and secondary excited electrons from atoms in the solid. This theory gives us sound theoretical background and practical tools to study EELFS spectra.

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