No abstract available

[en] Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions, the layer longitudinal magnetizations and quadrupolar moments of a spin-1 Ising film and their averages are examined. These quantities as functions of the temperature, the ratio of the surface exchange interactions to the bulk ones, the strength of the transverse field and the film thickness are calculated numerically and some interesting results are obtained. (author)

[en] The phase transitions of a ferromagnet spin-1/2 Ising superlattice consisting of two different materials in a transverse field is examined with the use of effective field theory that accounts for the self-spin function correlation. The critical temperature of the system is studied as a function of the thickness of the constituents in a unit cell and of exchange interactions in each material. A critical interface exchange interaction above which the interface magnetism appears is found. The effects of a uniform transverse field and the interface exchange interaction on the parameters of the system are also investigated. (author)

[en] In this paper, we discuss the behavior of conformal field theories interacting at a single point. The edge states of the quantum Hall effect (QHE) system gives rise to a particular representation of a chiral Kac-Moody current algebra. We show that in the case of QHE systems interacting at one point we obtain a 'twisted' representation of the current algebra. The condition for stationarity of currents is the same as the classical Kirchoff's law applied to the currents at the interaction point. We find that in the case of two discs touching at one point, since the currents are chiral, they are not stationary and one obtains current oscillations between the two discs. We determine the frequency of these oscillations in terms of an effective parameter characterizing the interactions. The chiral conformal field theories can be represented in terms of bosonic Lagrangians with a boundary interaction. We discuss how these one point interactions can be represented as boundary conditions on fields, and how the requirement of chirality leads to restrictions on the interactions described by these Lagrangians. By gauging these models we find that the theory is naturally coupled to a Chern-Simons gauge theory in 2+1 dimensions, and this coupling is completely determined by the requirement of anomaly cancellation. (author)

[en] The problem of finding the ferromagnetic and antiferromagnetic ''broken symmetry'' solutions of the correlated lattice fermion models beyond the mean-field approximation has been investigated. The calculation of the quasiparticle excitation spectrum with damping for the single- and multi-orbital Hubbard model has been performed in the framework of the equation-of-motion method for two-time temperature Green's Functions within a non-perturbative approach. A unified scheme for the construction of Generalised Mean Fields (elastic scattering corrections) and self-energy (inelastic scattering) in terms of Dyson equation has been generalised in order to include the presence of the ''source fields''. The damping of quasiparticles, which reflects the interaction of the single-particle and collective degrees of freedom has been calculated. The ''broken symmetry'' dynamical solutions of the Hubbard model, which correspond to various types of itinerant antiferromagnetism have been discussed. This approach complements previous studies and clarifies the nature of the concepts of itinerant antiferromagnetism and ''spin-aligning field'' of correlated lattice fermions. (author)

No abstract available

[en] We investigated numerically the critical scaling and universality in the short-time dynamics for the spin models on the two-dimensional triangle lattices. By using the dynamic Monte Carlo simulations, the critical exponents θ, z and β/ν are estimated from short-time dynamic scaling relations and the power-law behavior of the magnetization, auto-correlation and the second magnetic moment. Our results confirmed the universality proposal. (author)

[en] Acoustoelectric effect in semiconductor superlattice (SL) has been studied for a hypersound in the region ql >> 1. A nonlinear dependence of the acoustoelectric current j^ac on the constant electric field E is observed. It is noted that when the electric field is negative the current j^ac rises, reaches a peak and falls off. On the other hand, when the electric field is positive the current decreases, reaches a peak and then rises. A similar observation has been noted for an acoustoelectric interaction in a multilayered structure resulting from the analysis of the Si/Si/O₂ structure. The dominant mechanism for such a behaviour is attributed to the periodicity of the energy spectrum along the SL axis. (author)

[en] We compute the phase diagram of the nonmetallic compounds ZnCr2_pA1_2-2pS(Se)₄ (I[S,Se]) and Zn_1-pCd_pCr₂S(Se)₄ (II[S,Se]). We consider the bond-diluted Ising model on the spinel B site (S.B.S.) lattice with competitive exchange interactions, i.e. the ferromagnetic exchange interaction J₁ between nearest neighbours (n.n.) and the antiferromagnetic superexchange interaction J₂ between next-nearest neighbours' (n.n.n.) (and/or the more distant superexchange interactions J_i (i > 1). Dilution and competition are found to be responsible for the spill glass phase and the percolation behaviour. (author)

[en] Previous neutron-scattering research on solid heliums has been restricted to small momentum transfers, Q, both by large Debye-Waller factors and by scientific interest being restricted to collective modes and their interactions. It has also been limited by insufficient sources of neutron beams of about an electronvolt in energy, which are required to apply the method of deep inelastic scattering to solids. making use of a spallation neutron source and a suitable chopper spectrometer, one can now collect data in which the dynamic structure factor S(Q,E) directly reflects the atomic-momentum distribution n(p). For ⁴He, the major number density, samples of hexagonal close-packed (hcp), body-centered cubic (bcc), and normal liquid show identical S(Q,E)'s for Q's near 200nm^-1, at current levels of precision. The case of bcc ⁴He is used to illustrate the method, and the derived kinetic energy is compared with theoretical predictions. The applicability of these results in other areas of solid-helium physics is indicated. (39 refs., 9 figs.)