It is indicated that the system size effect performs an important role in the property of dynamical fluctuation in the nonlinear stochastic system far away from equilibrium. In Schlögl’s bimolecular reaction model, the properties of dynamical fluctuation show a distinctive feature depending on the value of index β which satisfies the relation V=(1⁄k)^β, where V is the system volume and k is a measure of the distance from equilibrium. When β>1.0, these properties show the classical feature. On the other hand when β<1.0, some peculiar phenomena essential in the nonequilibrium stochastics of nonlinear system are observed in the transition region far away from equilibrium as a result of system size effect.

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A new perturbative approach to a single-impurity Anderson model is presented. The on-site Coulomb repulsion is assumed to be infinite. With the use of the operator introduced by Hubbard, the perturbation expansion is made in terms of hybridization without the use of a boson field. This leads to a 1⁄N_f, expansion, where N_f is the multiplicity of the orbital degeneracy of the localized electron. In the lowest order of 1⁄N_f, the result coincides with that obtained by the variational or the boson methods.

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The symmetry relation of magnetoconductance (MC) with respect to magnetic field reversal plays an essential role in the quantum transport phenomena in microstructures. The symmetry of a ring with leads under the measuring condition of a two-terminal element is studied by two methods: (i) Landauer formula and (ii) the method of local electric field fluctuation, which adequately explains the asymmetry of MC in microstructures. We find that the Landauer formula is not applicable to the symmetry properties of MC in two terminal elements, whereas our method leads to symmetric conductance, i.e. G(H)=G(−H). The origin of the difference in the two formulae is discussed.

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It has been shown that the superconducting transition temperature, T_c, of M substituted YBa₂(Cu_1−xM_x)₃O_7−δ is markedly enhanced by low-temperature annealing in high-pressure oxygen gas, being essentially the same as that of the undoped one up to x=0.035, in cases of M=Fe and Co, while in cases of M=Zn and Ni, T_c is almost unchanged by the annealing. Since Co replaces only Cu1 and Fe replaces both Cu1 and Cu2, the results indicate that the superconductivity is affected little by the magnetic impurities substituting both the two Cu sites, as in the case of the Y substitutions with rare earth elements, while it is crucially affected by Zn. The result may prove that the Cooper pairs do not run on copper ions in this material.

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Zero-field cooled (ZFC) and field cooled (FC) magnetizations have been measured on the spin- and cluster-glasses of iron intercalation compound Fe_xTiS₂ (x=0.1–1⁄3) over the temperature range 4.2–150 K. We have found appreciable field cooling effects in both spin- and cluster-glass phases. From the observed ZFC and FC curves, strong anisotropies in the paramagnetic Curie temperature and effective magnetic moments are found, for which a qualitative discussion is given.

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Computer simulations have been performed to confirm predictions of the scaling theory which describes crossover behavior from isotropic to anisotropic cluster growth for the generalized diffusion-limited aggregation (η-model) on a square lattice. Results for the generalized diffusion-limited aggregation with η≤2 are found to be in qualitative agreement with the theoretical predictions. However, those with η=3 are inconsistent with the theory.

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In a series consisting of +1 and −1, a pair of the i-th and j-th elements, a(i) and a(j), is characterized by two integers; one is the separation m=j−i (j>i) and the other is the sum d of m−1 numerals between the two elements. If the pair is denoted by [a(i), a(j); m, d], all pairs in a series belong to one of the following four types for given parameters m and d: [1, 1; m, d], [1, \bar1; m, d], [\bar1, 1; m, d] and [\bar1, \bar1; m, d], where 1 and \bar1 are used instead of +1 and −1. Out of these four types, it has been verified that two types of pairs [1, \bar1; m, d] and [\bar1, 1; m, d] appear alternately in any series and therefore the total numbers of pairs are equal to each other for these two types or are different at most by unity. This correlation is applied to a layer structure such as Laves phase, and specific relations are derived.

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The Hirota bilinear method is applied to a weakly perturbed system and the stability of the soliton with respect to the bending of wavefront is studied. This method is more useful for stability analysis than the ordinary perturbation method or the perturbation treatment of the inverse scattering method.

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The polarization reversal process in the surface-stabilized ferroelectric liquid crystal was studied with a polarizing microscope utilizing a stroboscopic method. Domain patterns appearing during the polarization reversal were analyzed in terms of the spatial correlation function based upon the Avrami model of the crystal growth.

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A time-dependent variational principle is given for nonequilibrium density matrix of a quantum system. It allows a derivation of dynamical equations for thermodynamical forces which are the Lagrangian parameters of the present theory. If the system is near equilibrium, these equations determine the transport coefficients which satisfy the reciprocity relations. For the understanding of irreversibility, the introduction of the van Hove parameter turns out to be essential, which bases upon a distinct separation of microscopic and macroscopic scales in time.

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A new scheme of the coherent-anomaly method (CAM) is proposed to study critical phenomena in the models for which a mean-field description gives spurious first-order phase transition. A canonical series of mean-field-type approximations are constructed so that the spurious discontinuity should vanish asymptotically as the approximate critical temperature approachs the true value. The true value of the critical exponents β and γ are related to the coherent-anomaly exponents defined among the classical approximations. The formulation is demonstrated in the two-dimensional q-state Potts models for q=3 and 4. The result shows that the present method enables us to estimate the critical exponents with high accuracy by using the date of the cluster-mean-field approximations.

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A likelihood method is proposed for analysis of events which are produced in the hadron-hadron collision accompanied by the missing transverse momentum. The kinematical reconstruction is made by assuming variables sufficient to define the kinematics, and the likelihood of the assumption is evaluated by using the structure functions, the differential cross sections for intermediate states and the decay rate for final state configurations. The capability of the method is examined for simplified models of events including one- and two-missing massless particles. It is shown that (a) when events are well identified, dynamical parameters involved in the process can be determined, and (b) in new particle searches, narrow mass spectrums are obtained.

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The fine and hyperfine structure intervals of 2³P and 2¹P states of ³He are calculated by use of 165-term Hylleraas type wavefunctions. For 2³P the levels denoted by |JF⟩ are found to be |2, 5⁄2⟩, |1, 3⁄2⟩, |1, 1⁄2⟩, |2, 3⁄2⟩ |0, 1⁄2⟩ in the ascending order of energy and the corresponding intervals are 1781.0, 4512.2, 668.2 and 27413.5 MHz. ³P₁ and ³P₂ are hybridized strongly into |1, 3⁄2⟩ and |2, 3⁄2⟩. In ¹P₁ |1, 1⁄2⟩ is above |1, 3⁄2⟩ by 20.3 MHz. The accuracy of the calculation is checked and it is found that the maximum error may interfere the digit of 1 MHz.

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On the basis of 165-term Hylleraas type wavefunctions, the total energies of 2³P and 2¹P, the relativistic and the mass corrections, and the fine and hyperfine structure are calculated for the helium isoelectronics (from ³He to ²¹Ne⁸⁺) having nuclear spins I=1⁄2. 1 and 3/2. The accuracy of the calculation is examined by comparing the results with the experimental data for fine structure splitting of all the ions and for the hyperfine splitting of ⁶Li⁺ and ⁷Li⁺. Complete tables of the hyperfine structures are given for all the ions. The effect of ¹P–³P mixing is discussed.

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The nonlinear pressure wave propagation in a straight thin elastic tube having a slowly varying radius and containing an incompressible fluid is considered. The motion of walls is represented by that of the middle surface by the shell theories which are extended to the second order of the displacements. Nonlinearities being taken into account are due to the convective motion of fluid, nonlinear strains and stress-strain relations. By assuming some asymptotic state, the systems of basic equations are reduced to the perturbed Korteweg-de Vries equation in which perturbation terms represent the effects of the variation in the tube radius and dissipation. It is shown that the taper effect influences remarkably the pressure wave propagation.

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It is shown that the E_rf×B drift for resonant electrons in tokamaks does not cancel and forms an inward flux during rf heating with a travelling wave type spectrum when Dawson like treatment of Landau damping in the presence of the magnetic field is performed as an initial value problem, where E_rf is rf electric field and B is the magnetic field. This effect could be the basis of the phenomenon that the plasma confinement is improved during low density lower-hybrid current drive in tokamaks.

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Equilibrium (θ=constant) field configuration of the toroidal Z pinch ZP-2 is investigated by means of magnetic probes inserted in a plasma, for discharges of a plasma current below 22 kA. Field and current profiles agree with a modified Bessel function model. Field fluctuations, observed throughout the discharge, are investigated in relation to spontaneous generation and regeneration of the field flux. Spontaneous generation of the field flux results from time evolution of the local toroidal field produced by helical deformation of the plasma. Regeneration of the field flux is accompanied with relaxation field fluctuations of m=0 and m=1. For discharges of plasma current of 40 kA, the plasma of electron temperature of 90 eV and average electron density of 5×10¹³ cm⁻³ is obtained.

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The crystal structure of LiCsSO₄ was studied at 25, 0, −20 and −40°C in the normal phase and −71, −78 and −100°C in the ferroelastic phase by using X-ray reflection data collected by an automatic four circle diffractometer. The librational motion of SO₄ is highly anisotropic in the high temperature phase. Temperature variation of the atomic position of S or O atoms was small in the low temperature phase. The mutual proportionality between the temperature dependence of observed structure factors of reflections 201, 203, 205, 311 and 131 and that of the deviation angle Δγ of the monoclinic angle γ from 90° was found, which suggests that the phase transition is characterized by the order-disorder nature of the SO₄ ion coupled with the shear strain x₆.

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The shape of voids in quenched β-brass has been studied by means of transmission electron microscopy. A variety of void shape is found, while the void image calculated by using the two-beam dynamical theory can verify that the fundamental shape is a rhombic dodecahedron with the {110} faces. The variety is arisen from two factors. One is truncation of the ⟨100⟩ corners of voids and the other is deformation from the rhombic dodecahedron. From the truncation, the anisotropy of surface energy of β-brass can be estimated to be γ¹⁰⁰⁄γ¹¹⁰≥1.24. The deformation is due to void growth associated with the formation of antiphase boundaries.

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A neutron study of the static structure as well as the lattice dynamics was carried out on quenched α-Ag₃SI in the temperature range between 90 and 290 K. A distribution of silver ions among a disordered lattice formed by I and S was found to vary with temperature by the analysis with a least squares refinement of the structure. Phonon dispersion curves of low energy modes showed a slight temperature dependence. Dispersionless broad peaks were observed at 4∼5 meV, which seem to be a second harmonic of a local vibration mode clearly observed at 2∼2.5 meV. It is quite difficult to discuss the dynamics of atomic motions in detail from the phonon data because of a strong anharmonicity due to the disordered arrangement of anions.

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Structure factors of 9 icosahedral clusters were calculated. Icosahedral clusters discussed are 12 atoms at five-fold symmetry sites C₅ (icosahedron), 20 atoms at C₃ sites (dodecahedron), 30 atoms at C₂ sites, 60 atoms at mirror sites, 12 and 20 atoms at C₅ and C₃ sites (triacontahedron), 12 and 30 atoms at C₅ and C₂ sites, 30 and 20 atoms at C₂ and C₃ sites, 12, 30 and 20 atoms at C₅, C₂ and C₃ sites (star-shaped polyhedron), and 12, 30Al and 12Mn atoms at C₅, C₂ and C₅ sites (Mackay 54). Furthermore, the structure factors of quasicrystal obtained by the projection from the 6-dimensional cubic lattice are calculated. A comparison of the calculated electron-diffraction-intensity with the experimental one gives the unit length τ times the Al–Al bond length (τ=(\sqrt5+1)⁄2: the golden ratio).

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The crystal structure of [N(CH₃)₄]₂ZnBr₄ was studied at 25°C in the normal phase and 13, 11, 6, 1.5, −10, −40 and −100°C in the ferroelastic phase by single crystal diffractometry. The split-atom method and the significance test showed that the constituent ions are in disorder in the normal phase. In the ferroelastic phase, positional and thermal parameters and occupation probabilities of ions were determined. The structure in the ferroelastic phase is characterized by two kinds of chains composed of ZnBr₄ and N(CH₃)₄-1; one kind of which is along the c-direction, while the other kind is along the a-direction.

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The phonon dispersion relations in ferromagnetic Invar alloys, Fe₃Pt and Fe₆₅Ni₃₅, have been measured along the high-symmetry directions. The temperature as well as wave number (q) dependence of the phonon frequency shift, the linewidth in [110] TA₁ mode, have been observed. The results of these observations characterize the Invar problems. The relatively weak forces between nearest neighbor Fe atoms are responsible for the appearance of the soft mode in fcc Fe Invar alloys, according to the force constant analyses of the observed dispersion curves.

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Effects of interchain coupling on soliton dynamics are studied analytically based on the model describing, e.g., ferromagnet chains with planar anisotropy or DNA double helices. In the framework of the perturbation theory the interaction of solitons belonging to different chains is investigated, a coupling constant being a small parameter. In particular, the interaction energy of the solitons is calculated, and it is demonstrated analytically that two slow solitons can form a bound state. Some radiative effects accompanying the soliton bound-state dynamics are considered by means of the perturbation theory based on the inverse scattering technique. It is also demonstrated that the slightly excited bound state of the solitons emits the longitudinal vibrations in the framework of a more general model used in the DNA theory.

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The kinetic process of the incommensurate-to-commensurate phase transition in Rb₂ZnCl₄ has been investigated by the measurements of the time evolution of polarization and dielectric constant during the field-induced transition. The following picture of the phase transition has been obtained. Under a sufficiently strong dc field, the discommensurations (DC’s) are annihilated successively and the number of DC’s decreases. The lattice spacing increases and at the same time the DC lattice becomes considerably disordered. When the lattice spacing has increased to a certain threshold value, regions of the commensurate phase start to appear, they grow and finally cover the whole crystal. The above picture agrees with the result of theoretical study based on the free energy of a system undergoing a first-order commensurate-incommensurate transition.

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We discuss the improvement of the imperfect argument of Schuster for the absence of spin glass ordering at and below four dimensions in short-range continuous spin systems, and propose a condition for his method to be justified. Assuming satisfaction of the above condition, we apply the method to long-range interactions to reproduce the phase diagram drawn by a renormalization group approach. In particular the three-dimensional RKKY system is found to be at the lower critical dimension. Effects of exchange and uniaxial anisotropies are discussed. The latter anisotropy is shown not to induce transverse spin glass ordering if the system is not ordered in the xy-plane by the exchange interaction.

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The theory of the successive phase transitions in NaCN and KCN is presented. The elastic and electric dipole moments of a CN⁻ ion are treated in a unified way using the symmetry adapted orientational variables with E_g, T_2g and T_1u symmetries. Taking into account of the electronic polarizability of CN⁻ and K⁺ ions, the ground state of the electric dipolar arrangement is examined. It is shown that the electronic polarizability of a K⁺ ion α_K plays an essential role and that the experimentally observed antiferroelectric arrangement has the lowest energy when α_K>3.5 ų. The successive phase transition and the temperature dependence of the order parameters are examined.

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The Curie-Weiss law of the dielectric susceptibility χ in ferroelectrics is shown to be derived from two different mechanisms in the self-consistent phonon approximation: One is the increase in the correlation between dipoles which is related to the magnitude of the electrostatic interaction D. The other is the decrease in the mean square amplitude of the soft mode, which leads to the Curie-Weiss law through the rate of increase 1⁄t₀ of an individual susceptibility with the decreasing effective “dipole moment”. The dependence of χ on temperature has been numerically computed to investigate the dependence of the Curie constant on t₀ and D. The ratios of the paraelectric moment to the saturation moment have been evaluated from available experimental data in ferroelectrics. Deviations of these ratios from unity in displacive type ferroelectrics are explained in terms of t₀.

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The anisotropy of thermal expansion coefficients of RbLiSO₄ single crystal was measured by the dilatometric method. Anomalies along the b and c axes are larger than that along the a axis and those around the incommensurate phase are anomolously large. The thermal expansion coefficient along the c axis have a minus sign in the temperature range in which the successive phase transitions is observed. Ferroelasticity in the phase III is confirmed by the observation of domains which are able to moved easily by the shear stress.

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The phenomenological lattice gas model describing an adsorbed system on a rectangular substrate lattice is considered. A long range repulsive adatom-adatom interaction mediated by substrate atom displacements appears effectively. Accompanied by a surface reconstruction of striped pattern the adsorbed system shows, at the ground state, the phenomena known as the devil’s staircase; infinitely many commensurate phases appear successively with chemical potential.

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It is shown that the Ward identity should be taken into account in the calculation of the pinning frequency in the weak-pinning case. Otherwise, a strict condition for stability of the phason, i.e., for the pinning frequency being real is obtained. The calculation which satisfies the Ward identity is shown to guarantee the phason stability without any condition. The result represents that the phason is pinned by impurities no matter how weak the pinning potential is.

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The present approach to the above problem is essentially identical with Watson’s, except that his simple crystalline potential is replaced by a complicated one in order that the effect of the six surrounding Mg²⁺ ions might be taken into account more faithfully. The “2p” orbitals of O²⁻ are assumed to have a mixed character between “p” and “f” not as usual, while both “1s” and “2s” to have the pure “s” character as usual. The obtained “2p” orbitals differ very much in shape from existing ones. It is confirmed that the use of the new set of orbitals leads to the description of MgO that is almost free from the difficulty pointed first by Aikala et al.

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We have investigated the 3D–2D crossover of the localization effect in a system of heavily arsenic doped polycrystalline silicon films with thickness 40 to 1350 Å. The films with d≤220 Å show a log T dependence of the conductance. For a 220 Å film, ∼60% of the quantum correction to the conductivity is attributed to the electron-electron interaction effect, and the rest to the localization effect. Analyses of the magnetoconductance behavior have indicated that a weak spin-orbit scattering should be taken into account in the localization effect; a feature not observed in n-type bulk Si. The diffusion length of the spin-orbit scattering is estimated to be 0.28 μm. The inelastic scattering time τ_in for the 220 Å film varies as T^−0.95, indicating that the electron-electron scattering is the dominant phase breaking process in the present dirty 2D systems.

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Electrical resistance, R, Young’s modulus, E and internal friction, Q⁻¹ in (TaSe₄)₂I were measured simultaneously as functions of temperature and dc-electric field strength, using a resonant flexural vibration technique. The CDW elasticity around the phase transition was investigated, and the predicted scaling relation was partly found. Change in R due to the CDW motion is always accompanied by change in E. In addition to the nonlinear conductivity just above the threshold dc-bias, V_T (9.5 mV(41 mV·cm⁻¹) at 250 K), a transient behavior was found below very low dc-bias, V₀(<0.25 mV at 250 K), and an increase in R, a strong decrease in E and an increase in Q⁻¹ were observed at high dc-bias (>0.3 V at 250 K). The former is attributed to the reversible atomic rearrangement in CDW domain walls, and the latter to some viscous motion of impurity atoms or lattice defects relative to neighboring chains. The temperature dependence of V_T between 120 K and 250 K was found to follow the relation, V_T∝exp (T₀⁄T), where T₀ is a constant.

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The Madelung energy in the (Y, Ca)(Ba, La)₂Cu₃O_6+δ system has been calculated in order to find the distribution of hole carriers among sites. We regard the compoundas a superconductor, when the lowest-energy distribution is such that holes enter sites in CuO₂ sheets, whereas we regard it as a semiconductor, when no holes enter sites in the CuO₂ sheets. Based on this criterion, we find a phase diagram, where the superconducting region is separated from the semi-conducting region by a boundary. A good agreement with the experimental finding by Tokura et al. is obtained, when account is taken of the ordering of exygen vacancies in the basal plane of Fig. 1 in the text. It is found that for some compounds with small δ (∼0.25), holes are spontaneously produced in CuO₂ sheets, so that the compounds may be a superconductor although their nominal hole content is zero.

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Ferromagnetic resonance of epitaxially grown Mn/Sb multilayered films is studied between 4.2 and 270 K. The resonance field depends systematically on the MnSb layer thickness ranging from 3.6 to 43 Å. Uniaxial anisotropy constants, K₁ and K₂ are determined for each sample from the angular dependence of the resonance field. The easy axis for the magnetization turns from in the plane of the film to along normal to the film for the thickness less than 7.2 Å at 4.2 K. A possible interfacial effect on the change of the easy direction is proposed.

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We systematically study the spin 1/2 quantum XXZ model on the square lattice using a quantum Monte Carlo method. The temperature dependence of the energy, specific heat and order parameter is calculated for the systems of sizes up to 16×16. Investigating the size dependence carefully, we exarnine the ground-state energy and the existence of the long-range order.

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The thermoelectric power and the resistivity for the Ce-Kondo system are precisely calculated at low temperatures. The local Fermi liquid theory is extended to the case including the crystalline field in order to precisely evaluate the thermoelectric power with the aid of the Bethe Ansatz method. The characteristic properties caused by the crystal-field effects are investigated for the above quantities. The anisotropic properties are discussed briefly for the hexagonal and tetragonal fields.

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Copper sulfate pentahydrate CuSO₄5H₂O is investigated by ESR at 9, 17, 24, 35 and 50 GHz regions down to about 100 mK using a combined cryostat of ³He and adiabatic demagnetization.
The temperature dependent exchange interaction J_AB between inequivalent site spins A and B is found. It is about 0.11 K at room temperature and increases with decreasing temperature up to 0.24 K. Temperature dependent resonance shifts are attributed to the exchange shift coming from non-resonant dissimilar spins. Partial order effect below 1 K is discussed.

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¹⁴N NQR frequencies and T₁’s were measured between 54 and 150 K in crystalline trans-azobenzene which has two different molecular sites, orientationally ordered and disordered, at room temperature. The NQR parameters at 77 K were determined to be e²Qq⁄h=5.0150 MHz and η=0.4231 for the ordered site, and e²Qq⁄h=4.9619 MHz and η=0.4060 for the disordered site. The fine structure of each resonance line was observed by the Fourier transform method. It changes abruptly around 90 K, indicating the existence of a phase transition. The fine structures and their change at the phase transition can neither be attributed to the intramolecular dipole interaction between the two nitrogen nuclei, nor to crystallographic inequivalency of the molecules in the unit cell.

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NMR measurements of Cl nuclei were carried out to clarify the covalency between Cr²⁺ and Cl⁻ ions. By analyzing the NMR spectra, the unpaired spin densities of s- and p-orbitals of Cl⁻ ion are estimated to be f_s=0.21% and f_σ−f_π=−1.1%. Contrary to what was anticipated, the π-bonding is stronger than the σ-bonding.

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The temperature dependence of the conduction-electron-spin-resonance g value, linewidth and peak height in aluminum has been measured with a foil of 16.4 μm, at 22.6 GHz, from 1.9 to 110 K. The full temperature variation of the linewidth has been explained by the semiquantitative theory of Silsbee and Beuneu with g anisotropy. The orbital scattering mechanism responsible for the spin relaxation has been confirmed to be different from the conventional resistivity scattering, and the phonon scattering rate has shown the temperature variation as T³ at lower temperatures and T² at relatively higher temperatures. The temperature variations of the g value and peak height have both shown nonmonotonic behavior, supporting the “two-spin model” in which electrons in second and third Brillouin zones are partially decoupled from one another.

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To understand the isotope effect in the ferroelectric phase transition of CsH₂PO₄ and CsD₂PO₄, a quasi-one-dimensional model is proposed. In contrast to the existing models which consider only either the proton’s degree of freedom or the polarization dipoles, both of them are regarded as essential elements of the system, while the tunneling protons are assumed to have nothing to do with dielectric polarization. The static dielectric constant, calculated on the assumption of no tunneling for CsD₂PO₄ and a finite tunneling frequency for CsH₂PO₄, reproduces well the experimental data by using model parameters consistent with the saturated polarization data. The model predicts absence of soft modes despite proton tunneling, in agreement with the order-disorder behavior of the phase transition as has been confirmed by experiments.

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We have studied the optical properties of Al_xGa_1−xAs-AlAs ternary alloy multiquantum-well structures around two Γ−X crossovers by means of photoluminescence and absorption saturation. In the photoluminescence, the peak due to the n=1 heavy exciton (Γ−Γ) is observed for Al composition x from 0 up to 0.34. When x is 0.34 or more, another kind of the peak due to the Γ−X recombination (recombination between an X-electron in AlAs and a Γ-hole in Al_xGa_1−xAs) is observed in the low energy side, corresponding to the first Γ−X crossover. In the absorption saturation experiments, on the other hand, the saturation was observed in all the samples except the Al_0.51Ga_0.49As-AlAs sample corresponding to the second Γ−X crossover. The fact suggests that Γ-electrons relax to the X-state is the Al_xGa_1−xAs alloy very quickly compared with the other relaxation processes such as the Γ−Γ recombination in Al_xGa_1−xAs and the transfer of a Γ-electron in Al_xGa_1−xAs to X-state in AlAs.

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Time-resolved luminescence and time-resolved ODMR measurements have been carried out on a-Si:H/a-Si_1−xN_x:H superlattices and electron-hole recombination processes in these superlattices have been studied. Nonradiative recombination is suppressed in the superlattices by its two-dimensional feature when the well-layer thickness, L_w, is much smaller than the average spatial separation of dangling bonds. Radiative recombination is enhanced by an increase in density of electrons and holes due to the confinement effect. But the radiative recombination rate is reduced by its two-dimensional feature when the well-layer thickness is very small (L_w<10 Å). The time-resolved luminescence spectra shift towards higher energy and are broadened with decreasing L_w. These results are explained in terms of a quantum-well model.

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Raman scattering from one- and two-magnon excitations in various rare-earth orthoferrites are studied. The magnetic in-plane and out-of-plane anisotropy energies of these systems are obtained and discussed based on the two-sublattice model of ironspins. Detailed temperature dependence of the frequencies of two k≅0 magnons are also examined on YFeO₃, ErFeO₃, SmFeO₃, Er_0.7Sm_0.3 FeO₃ and DyFeO₃. It is shown that the softening behaviors of one-magnon peak frequencies are different between the rotational- and abrupt-type spin-reorientation (SR) systems. This is explained by different anisotropy terms which contribute to the magnon softening associated with SR transitions. The exchange interactions between the iron and rare-earth ions are considered to interpret the magnon softening in the vicinity of SR temperatures. The temperature and polarization properties of two-magnon Raman spectra are also discussed.

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By point by point measurements, the reflectivity spectra of Y₃Al₅O₁₂ (YAG) single crystals have been obtained. Their spectral shapes as well as absolute magnitudes appear correct over the region up to 40 eV and yield the reasonable value of the effective number of electrons per unit cell. A new spectral position of the tail absorption intrinsic to YAG at room temperature is also reported.

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The intensity of the F center emission in KCl is reduced by simultaneous irradiation of 1.06 μm pulse from an Nd:YAG laser, whose second harmonic pulse is used for the F excitation. The reduction is related to the stimulated emission in the relaxed excited state of the F center. The cross section of the stimulated emission is estimated to be 4.0×10⁻¹⁷ cm² at 80 K.

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Reaction-limited cluster-cluster aggregation in systems with two types of particles (A and B) has been studied in two and three dimensions using computer simulations. A simple model is used in which bonding can occur between pairs of unlike particles (A–B) but not between like particles (A–A or B–B). For values of the concentration ratio (f=ρ(A)⁄(ρ(A)+ρ(B)) which are either too large or too small, the aggregation process cannot proceed indefinitely. The fractal dimension of large clusters is independent of f but the aggregation kinetics is sensitive to f.

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