International Journal of Modern Physics B

The Ginzburg–Landau (GL) theory is recast using a Hamiltonian involving the complete kinetic energy density which requires that the surface energy must contain a term ∇|ψ|² to support superconducting (SC) states. The GL equations contain two temperature t dependent parameters α(t) and β(t), which are respectively the coefficients of the SC pair density ∝|ψ|², and the pair interaction term ∝|ψ|⁴ in the free energy density. The sign of these parameters, which defines distinct solution classes, and the ratio are governed by the characteristics of the surface energy density. In addition to the conventional bulk superconducting states with (α < 0, β > 0), anomalous superconducting states exist for all other sign combinations, including cases with β < 0 which may exist only when surface pair interactions are significant. All possible solutions of our generalized nonlinear, one-dimensional GL equations are found analytically and applied to a thin superconducting slab which manifests the possibility of states exhibiting enhanced, diminished, and pre-wetting superconductivity. Critical currents are determined as functions of s(t) and surface parameters. The results are applied to critical current experiments on SNS systems.

The present paper focuses on the tapered planar waveguide solution for an initial given wave form. The algorithm is constructed in distributions space such that the calculations can be actually computed by taking some hypothesis regarding the mode series which appear. The whole argument leads to the conclusion that the wave is compressed towards the waveguide in the direction of tilting, leading thereafter to a focusing phenomena. We present two alternative constructions in order to compute the convolution which gives the wave inside the waveguide. The hypothesis are providing results in good approximation with the real evolution of the field within the definition domain.

The two level tunnelling model is applied to analyze recent experimental data on low temperature thermal conductivity of Cu_xSn_1-x metallic glasses. An extra scattering mechanism due to Rayleigh is introduced to describe three characteristic regions of conductivity. Model parameters are determined using least-squares fitting procedure. Results derived from the parameters allow one to predict several interesting low temperature properties of metallic glasses in particular the characteristic plateau of conductivity. Theoretical results are also compared and contrasted with those of other metallic and non-metallic systems, and both common and uncommon features that exist between them are discussed.

Binding energy for an exciton (X) bound in a parabolic two-dimensional quantum dot by an acceptor impurity A^- located on the z-axis at a distance d from the dot plane, are calculated using the Hartree formalism with a recently developed numerical method (PMM) for the solution of the Schrödinger equation. As our analysis indicates there is a critical dot radius R^c such that for R < R^c the complex (A^-, X) is unstable and with an increase of the impurity distance this critical radius increases. Furthermore, there is a critical value σ^c of the mass ratio such that for σ > σ^c the complex is stable.

We examine numerically the long-time average probability in a two-site system, for finding an electron staying at an initially occupied site for an asymmetric quantum Holstein electron-phonon coupled model. The principal finding is the existence of quantum-mechanical resonant tunnelling channels in the electron localization phenomenon. Based on a strong-coupling perturbative analysis, we have explained the presence of the channels as a consequence of a general resonant effect on an effective two-level system. Finally, a comparison of the quantum problem with the semiclassical description given by the Discrete Nonlinear Schrödinger equation is performed.

We present characteristic functions, thermal equation of state and heat capacity at constant volume for nondegenerate relativistic quantum gases without and with generation and annihilation of particle-antiparticle pairs. For some physical quantities, nonrelativistic and ultrarelativistic expressions are analysed.

The statistical modeling was used in the analysis of structures containing heterogeneous masses. The statistical probability of a system of coupled oscillators was found taking into account the mass dependence of energy levels. It is essentially a new approach. Both the low as well as high temperature expressions for diffusion coefficient were found. Comparison with experimental data gave satisfactory agreement.

Dynamic hysteresis property is a common phenomenon in FeSi materials under time-varied applied field. This paper presented a dynamic hysteresis model based on Preisach scheme. The rectangular-shaped elementary hysteresis operator with two states in classical Preisach model is replaced by a non-rectangular shaped one with multiple states. The output of each state is calculated by a cosine function. The proposed dynamic hysteresis model is experimently tested by comparing the simulated hysteresis loops to experimental ones. The model can be used to describe the dynamic hysteresis in FeSi material for magnetizing frequencies from quasi-static to several hundred Hertz.