Three glasses of Na₂O-TiO₂-P₂O₅ system were prepared by melting the appropriate amounts of Na₂CO₃, TiO₂ and (NH₄)₂HPO₄ in an open crucible. The DTA thermal analysis showed crystallization temperature decreases with increasing sodium content in the sample. The structures of the virgin and annealed glasses (at 900 K for 4 h) were studied using FT-IR, X-ray diffraction (XRD) and scanning electron microscope (SEM). Different crystalline phases depending on the compositions of the glasses were formed after annealing. The framework of the glasses was found to be made of PO₄, TiO₄ tetrahedral groups as well as TiO₆ entities that coexist with sodium modifier ions. TiO₂ enters the structure in tetrahedral or octahedral coordination in all samples. The temperature dependence of electrical conductivity, dielectric constant and dielectric loss for the virgin and annealed glasses is studied over a temperature range between 300 and 600 K and at a frequency from dc to 10⁶ Hz. Many breaks, depending on both the composition and heat treatment of the samples, are observed on the plots of ln σ vs. 1/T. The conductivity increased by annealing and the results were explained on the basis of hopping Na⁺ ions in the glass matrix. The ac-onductivity increased with frequency according to σ_ac(ω)=Aω^s, where s has a value in the range 0.4--0.8 depending on the temperature and the composition of the sample. The temperature dependence of the dielectric constant showed that at relatively lower temperatures the electric dipoles formed in the glasses are frozen and starting to rotate at higher temperatures. Each of ε^′ and ε^{′ ′} was found to be dependent on the composition and the crystalline phases formed in the matrix. All the results have been discussed and correlated together.

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The electronic structure of (Sc_1-xTi_x)Fe₂ with the hexagonal Laves phase (C14) structure is calculated self-consistently by LMTO-ASA method and the fixed spin-moment procedure. Ferromagnetic solutions with high- and low-moments are obtained together with the antiferromagnetic one over a wide range of composition and volume. It is shown that the magnetic moment of Fe on the 2a site in TiFe₂ vanishes in the low-moment ferromagnetic state, just as in the antiferromagnetic state, and grows up nearly to the size in the high-moment ferromagnetic state with increasing Sc concentration. The energy difference between the two ferromagnetic states is small and depends sensitively on the change in volume and leads to a considerable magnetovolume effect. A metamagnetic transition from the antiferromagnetic state into the high-moment ferromagnetic state is expected at the critical magnetic field of 145 T for TiFe₂. The composition dependence of the ferromagnetic moment for Ti_1-yFe_2+y near the stoichiometric composition is discussed in the context of the high- and low-moment ferromagnetic states.

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Single crystals of β^′-Cu_xV₂O₅ have been successfully grown by a self flux method, and their structural, magnetic, and electric properties have been systematically investigated as a function of T and x. The properties of β^′-Cu_xV₂O₅ are strikingly different from those of isostructural β-A_xV₂O₅ (A=Na, Ag, etc.). With increasing x, the electrical conductivity of β^′-Cu_xV₂O₅ along the b-axis increases monotonously and the metal-insulator transition occurs around x=0.60. The conductivity is highly anisotropic. For x < 0.43, the system undergoes a structural phase transition at ca. 200 K to an incommensurate (IC) phase. For x≈ 0.40, the IC phase undergoes another phase transition to a commensurate one. A significant decrease in the conductivity has been found at the latter transition. The explanations of the metal-insulator transition and the structural phase transitions have been given in terms of randomness and Cu-ion ordering, respectively.

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The conductivity, σ, of molten (AgI)_1-c(Ag₂S)_c mixtures decreases rapidly on the addition of AgI to Ag₂S. The σ of molten Ag₃SI is 13 ohm^-1 · cm^-1 at the melting point. It is suggested that a deep pseudogap is caused by the addition of AgI to Ag₂S. The thermoelectric power, S^*, of liquid Ag₂S is - 77 μV/K at the melting point. The S^* of molten (AgI)_1-c(Ag₂S)_c mixtures decreases gradually with increasing AgI component and reaches a minimum value of - 135 μV/K at the composition c=0.5. Moreover, the sign of S^* on the AgI-rich side changes gradually from negative to positive with increasing AgI composition. This p-n transition was found to occur near the composition c=0.36. The change in sign of S^* may be closely related to a gradual transition from predominantly electronic conduction to ionic one. The behaviour of σ and S^* for molten (AgI)_1-c(Ag₂S)_c mixtures was analysed by using a model of conduction processes due to both electrons and silver ions.

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The transport properties through a quantum dot are studied by using the finite-U Anderson model. The nonequilibrium Kondo resonance is investigated by the perturbation expansion in a power series of the Coulomb repulsion U in the dot at zero temperature. The current conservation is realized by the introduction of an effective distribution function in the dot. It is found that the Kondo peak in the density of states is not split by an applied voltage bias, which is in accord with the experiments to date.

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The conductivity measurements were performed in the spin-density-wave (SDW) phase of (TMTSF)₂ClO₄. The electric conductivity increases above the clear threshold electric field E_T. The normalized excess electric conductivity [σ(2E_T)-σ(0)]/σ(0) rapidly decreases below about T^*~= 0.3T_SDW, where T_SDW is the SDW transition temperature. In high electric fields far above E_T, the temperature independent electric conduction expressed as the function j=j₀exp (-E₀/E) is observed below T^*. It is suggested that the sliding of SDW with the quantum origin occurs in the low temperature. These phenomena are related to the phase transition dividing the SDW phase into two sub-phases in (TMTSF)₂ClO₄. The electric conductivity in the low temperature sub-phase is discussed in term of the SDW with the discommensuration.

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Reentrant first order and second order transitions are observed in thin TiN films under the paramagnetic limitation of superconductivity, where the temperature gradients of critical fields are positive. Then, the superconducting condensate has to have higher entropy than the normal state immediately below the critical fields. The observations of reentrant transition in thin TiN films above the tricritical point reveal that the renormalized Fermi liquid effect plays an important role for the superconducting transition. The antisymmetric Fermi liquid parameters obtained from the temperature dependence of critical field have positive definite values of 0.23. Spin orbit scattering parameters almost inversely increase with decreasing film thickness. Orbital depairing parameters are almost linear to the square of film thickness.

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Recent calculation found a new type of pairing states, i.e., a spatially oscillating d+s-wave symmetry, in the two-dimensional t-J model [M. Ogata: J. Phys. Soc. Jpn. 66 (1997) 3375.] The d+s-wave state is a possible candidate for electron-doped cuprates because the quasiparticle states in the bulk are fully-gapped reflecting the lack of nodes in k space. We calculate the local density of states near the surface for the case of d+s-wave symmetry. It is shown that a zero-energy peak shows up in the local density of states near a (110) surface, even though there is no nodes in the d+s-wave state. However, due to the absence of the nodes, we find that the zero-energy peak splits. This means that the d+s-wave state has a very unique character. The present result is compared with experimental data on Nd_1.85Ce_0.15CuO₄.

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One-dimensional quantum antiferromagnetism has been found in a tetragonal spinel oxide, GeCu₂O₄. Actually the temperature dependence of magnetic susceptibility exhibiting a broad maximum around 80 K can be well-described as that of S=1/2 Heisenberg antiferromagnetic chains with J/k_B=135 K. Cooperation of spin frustration caused by the triangular arrangement of the cupric ions at octahedral sites and the Jahn-Teller elongation of the CuO₆ octahedra along the c axis seems to lead to the formation of magnetically isolated CuO₂ chains made of edge-sharing CuO₄ squares. However, a small drop in susceptibility and also a sharp spike in specific heat suggesting the occurrence of long-range antiferromagnetic ordering are observed at 33 K. The effects of Si-for-Ge substitution and Mg-for-Cu substitution are also reported.

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Mean-field theory is insufficient to explain the magnetic order of RbFeCl₃ in a magnetic field applied in the c plane. Specifically, quantum and thermal fluctuations induce magnetic structures which do not otherwise appear, as found also for CsCuCl₃. We derive microscopically an expression for the free energy which describes both kinds of fluctuations on an equal basis. Our result includes mean-field theory, but goes beyond it to include terms which lift the nontrivial degeneracy. In addition to the modified 120°structure at low fields and the aligned state at high fields, we find an up-up-down-type collinear structure and a coplanar structure at intermediate fields. Our theory explains qualitatively experimental results at low temperatures, but detailed confirmation requires further experiments including the neutron scattering.

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Yb₄As₃ is a 4f compound showing a heavy-fermion-like behavior in spite of its low carrier concentration. Previous studies have shown that Yb³⁺ chains are formed along ‹ 111› below the charge ordering temperature T_c=290 K. In this paper an effective Hamiltonian to describe the low-energy physics of the Yb³⁺ chain is derived by properly taking into account its unique structure. The resulting Hamiltonian is surprisingly simple, showing a hidden symmetry previously unnoticed. In addition it gives a support to a recent work by Oshikawa et al., which emphasizes the importance of the Dzyaloshinsky-Moriya term. It is also pointed out that the structure of the Yb³⁺ chain leads to a mixing between the almost localized 4f state and the 5d electron-like carriers.

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We measured the heat capacity of an S = 1 Haldane compound NDMAZ under the pressure to investigate the three-dimensional magnetic ordering due to the anisotropy (D) and/or the interchain interaction. However, the experimental result shows that the Haldane gap (Δ) has been enhanced by the pressure and the magnetic ordering has not been observed. The remarkable increase of intrachain interaction (J) by the pressure will lead to the enhancement of Δ. We also discuss about the pressure-induced changes of Δ/| J | and D/| J | in this Haldane compound.

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Magnetic phase diagram of NiS_2-xSe_x has been reexamined by systematic studies of electrical resistivity, uniform magnetic susceptibility and neutron diffraction using single crystals grown by a chemical transport method. The electrical resistivity and the uniform magnetic susceptibility exhibit the same feature of temperature dependence over a wide Se concentration. A distinct first order metal-insulator (M-I) transition accompanied by a volume change was observed only in the antiferromagnetic ordered phase for 0.50≤ x≤ 0.59. In this region, the M-I transition makes substantial effects to the thermal evolution of staggered moments. In the paramagnetic phase, the M-I transition becomes broad; both the electrical resistivity and the uniform magnetic susceptibility exhibit a broad maximum around the temperatures on the M-I transition-line extrapolated to the paramagnetic phase.

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Three-dimensional geometrically frustrated itinerant magnet is investigated based on the single band Hubbard model on the pyrochlore lattice. The magnetic correlation and the quasiparticle properties are discussed by the weak correlation approach for half-filled case, based on the single electron spectrum in consideration of the lattice geometry. The spectrum reveals the existence of doubly degenerate flat band over the whole Brillouin zone. The spin fluctuation spectrum in RPA is anisotropic and shows the independence on frequency. The result is globally consistent with the observed in Y(Sc)Mn₂. It is also shown that the frequency spectrum is clearly different from the conventional Fermi liquid one, which brings the breakdown of the Fermi liquid picture owing to the divergence of quasiparticle mass.

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We have succeeded in growing the single crystal of a new ternary intermetallic uranium compound U₃Pd₂₀Si₆. It crystallizes in the Cr₂₃C₆-type cubic structure and the uranium ions are located on two different crystallographic sites. Two sucessive magnetic phase transitions are found at 19 K and 2 K in the electrical resistivity, specific heat and magnetic susceptibility measurements. These are attributed to antiferromagnetic and ferromagnetic orderings, respectively. The magnetic susceptibility obeys the Curie-Weiss law above about 50 K with the effective moment 3.30 μ_B/U and the magnetic entropy at 19 K is about R ln 3 per uranium ion. These results indicate that the 5f electrons in U₃Pd₂₀Si₆ are likely to be localized. We discuss the magnetic properties of U₃Pd₂₀Si₆ in comparison with those of R₃Pd₂₀X₆ (R=rare earth: X=Si, Ge).

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Electron spin resonance measurements on single-crystal and powder of GdAs have been performed in the temperature range from 4.2 to 40 K and in the frequency range from 55 to 585 GHz to obtain microscopic information about the magnetic structure. The results obtained indicate that GdAs is an “easy-plane” antiferromagnet with the magnetic moment lying in the (111) plane below Néel temperature ( -- 20 K). According to an analysis of mean field approximation, the exchange field and the out-of-plane anisotropy field have been estimated to be μ₀H_E=8.1 T and μ₀H_A=1.4 T, respectively. The transition field (H_c=2 H_E+H_A) from the antiferromagnetic to the forced ferromagnetic state is 17.6 T.

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We report the dielectric anomaries at the phase transitions of Lu(Fe²⁺ Fe³⁺)O₄, which is considered as a charge and spin frustrated system. Dielectric constant shows a hump, just above the transition from the high temperature two-dimensional to the low temperature three-dimensional charge ordering. A few glassy behaviors were observed at this transition. The presence of spontaneous polarization in the low temperature phase was confirmed by the measurement of pyroelectricity. A step-wise increase of the dielectric constant with increasing temperature was observed between 150 K and 250 K as in other RFe₂O₄. These phenomena are explained by the presence of the polar domains with the ordering of Fe²⁺ and Fe³⁺ and the motions of the antiphase boundaries between them.

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PbIn_1/2Nb_1/2O₃ (PIN) single crystal plates obtained by different thermal treatment were investigated by means of polarizing microscopic observations. It was found that, in an as-grown PIN (called partly disordered PIN), there is a coexistence state of the high and low temperature phases in a wide temperature range from 30 to 130°C. In the coexistence region, phase boundaries were observed to move according to temperature change, indicating that the phase transition temperature should distribute spatially in the sample plate. This distribution was also confirmed by the dielectric measurement made at several different spots (about 0.04 mm²) in the sample. The distribution of the transition temperature in the partly disordered PIN sample was discussed.

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The π-electronic excitations of the intercalated carbon nanotubes are studied within the linear response approximation. Intercalation would induce free carriers and thus a new intra-π-band plasmon with the lowest frequency ω_p--1 eV. The intercalated carbon nanotubes could also exhibit the π plasmon with the highest frequency ω_p>2γ₀ (the resonance integral γ₀-- 3 eV). These two plasmons are affected by the lattice constant, and the magnitude and the direction of the transferred momentum. The intercalation-induced plasmon is sensitive to the change in the free carrier density, but the opposite is true for the π plasmon.

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We theoretically study the lattice relaxation dynamics of a photogenerated single exciton which finally results in a macroscopic domain in insulating solids. Especially, we focus on three elementary nonlinear processes of this domain formation, which we call aggregation, growth and proliferation. This domain formation phenomenon is usually called `photoinduced structural phase transition' (PSPT). In these three elementary processes, the exciton does not stay within a single adiabatic potential surface but transits diabatically between the different potential ones. Hence, the full-quantum-mechanical treatment is indispensable. As one of the models for this type of phase transition, we consider a strongly coupled many exciton-Einstein phonon system. This is our relevant system. We also assume this system to interact with even and odd reservoir modes as well as photons. The even modes couple linearly with Einstein phonons and dissipate their energies, while the odd modes couple linearly with excitons and non-radiatively create and annihilate them. Furthermore, excitons are assumed to be strongly repulsive at the same sites, while attractive at the nearest-neighboring sites. The characteristic of our relevant system is the so-called multistable situation, where various multi-exciton states are energetically close to 1-exciton states. We also assume there is the third order anharmonic coupling between excitons, which naturally comes from the long-range Coulomb interaction and incomplete bosonic nature of excitons. Within the Markov approximation for reservoir modes and photons, the time evolution of the density matrix is numerically calculated. As a first work, we have shown characteristics of the early time dynamics of the formation of a domain, against various dissipation and relaxation processes. The importance of the aforementioned three elementary nonlinear processes are clarified. We conclude the multistability and the anharmonicity of exciton states are important for the occurrence of PSPT. We also conclude several ten excitons can be generated from one photogenerated exciton if these two characteristics are realized.

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Spatially resolved electron energy-loss spectra were measured from aluminum oxide fine particles of 10 and 55 nm radius. The impact parameter dependence of the surface plasmon generated between the surface of the particle and vacuum were revealed. The spectra due to the surface plasmon excitation of the fine particle of 10 nm radius are well explained by the local dielectric theory but those of 55 nm radius are not. This difference can be attributed to the relativistic effect applied for large size fine particles, which has been predicted by [Abajo: Phys. Rev. B 59 (1999) 3095].

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We measure 2p → 3d → 2p resonant X-ray emission spectra (RXES) of d⁰ system (ScF₃ and TiO₂) and analyze them by means of MX₆ (M=Sc or Ti, X=F or O, respectively) cluster model with full multiplet effects. We treat the whole RXES process as a coherent second order optical process and take the polarization dependence into account. The strong polarization dependence of the inelastic peak is clearly seen both in the experimental and calculated results. In order to clarify it, we investigate the detailed mechanism of the polarization dependent RXES by the total energy level diagram and the group theoretical consideration.

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