International Journal of Modern Physics B

General conditions for the occurrence of mesoscopic phase fluctuations in condensed matter are considered. The description of different thermodynamic phases, which coexist as a mixture of mesoscopically separated regions, is based on the theory of heterophase fluctuations. The spaces of states, typical of the related phases, are characterized by weighted Hilbert spaces. Several models illustrate the main features of heterophase condensed matter.

It has been argued in previous works by the authors that nodal excitations in (2 + 1)-dimensional doped antiferromagnets might exhibit, in the spin-charge separation framework and at specific regions of the parameter space, a supersymmetry between spinons and holons. This supersymmetry has been elevated to a N = 2 extended supersymmetry of composite operators of spinon and holons, corresponding to the effective "hadronic" degrees of freedom. In this work we elaborate further on this idea by describing in some detail the dynamics of a specific composite model corresponding to an Abelian Higgs model (SQED). The Abelian nature of the gauge group seems to be necessitated both by the composite structure used, and also by electric charge considerations for the various composites. We demonstrate the passage from a pseudogap to an unconventional superconducting phase, which notably is an exact non-perturbative analytic result, due to the underlying N = 2 supersymmetric Abelian gauge theory. We believe that these considerations may provide a first step towards a non-perturbative understanding of the phase diagrams of strongly-correlated electron systems.

We investigate the structural relaxation in a binary fluid over the time scales of β-relaxation regime. For this we have used a recently proposed self-consistent mode-coupling theory (MCT) formulated from the fluctuating nonlinear hydrodynamics approach. We have considered here both the hard sphere as well as the Kob–Andersen Lennard–Jones¹ binary mixtures. From the solution of the MCT equations obtained here the initial power law decay t^-a appears to be very weak. For the later part of the β-relaxation regime, the density correlation functions follow von Schweidler (VS) power law decay t^b. The validity of the so-called factorization property of the MCT over the β-relaxation is also analyzed. We find the exponent b to be in qualitative agreement with the findings from the computer simulations of the same system by Kob and Andersen.

The Embedded atom method has been used to investigate the strain field due to substitutional transition metal impurities in Ni. The calculations are carried out in the discrete lattice model of the metal using Kanzaki lattice static method. The results for atomic displacements due to 3d, 4d and 5d impurities (Cu, Pd, Pt and Au) in Ni are given up to 20 NN's of impurity and are compared with the earlier calculations and with the available experimental data. The maximum displacements of 3.6% of 1NN distance are found for NiAu, while the minimum displacements of 0.78% of 1NN distance are found for NiCu alloy respectively. The relaxation energy for Cu are found less than those for Pd, Au and Pt impurities in the Ni host.

We investigated the coherent states of nonconservative harmonic oscillator with a singular perturbation. The invariant operator represented in terms of lowering and raising operators. We confirmed that if the difference between two eigenvalues, α and β, of coherent states is much larger than unity, the states |α> and |β> are approximately orthogonal to each another. We calculated the expectation values of various quantities such as invariant operator, Hamiltonian and mechanical energy in coherent state. The mechanical energy of the system described by the Kanai–Caldirola Hamiltonian decreased exponentially depending on γ as time goes by in coherent state.

The critical temperature T_c of a weakly interacting Bose gas in an isotropic power-low potential is investigated in the mean-field approximation by taking into account the fact that the particle density distribution function appearing in the mean-field depends on the chemical potential. We derive the general formula of the shift of T_c from that of the ideal gas to the lowest order of an interaction. In three-dimensional space, we show that the shift of T_c changes its sign from a negative value for n < 3 to a positive one for n > 3, where n is the exponent of the power-low potential.

The unique characteristic of quantum mechanics may be used in the near future to create a quantum associative memory with a capacity exponential in the number of neurons. In this paper we discuss some quantum computational ideas and algorithms necessary to develop a quantum associative memory.

The generalization of the Jaynes–Cummings (GJC) Model is proposed. In this model, the electromagnetic radiation is described by a Hamiltonian which generalizes the harmonic oscillator to take into account some nonlinear effects which can occur in the experimental situations. The dynamical superalgebra and supercoherent states of the related model are explicitly constructed. Relevant quantities (total number of particles, energy and atomic inversion) are computed.

We present a detailed theoretical study of the influence of linearly polarized intense terahertz (THz) laser radiation on energy states of hydrogen-like impurities in semiconductors. The dependence of the binding energy for ground (1s) and first excited (2s) states, E_1s and E_2s, on the intensity and the frequency of the THz radiation has been examined for a GaAs-based system. It is found that E_1s, E_2s and E_2s-E_1s decrease with increasing radiation intensity or with decreasing radiation frequency, which implies that an intense THz field can enhance ionization of dopants in semiconductors. Our analytical and numerical results show that one of the most important results obtained by A. L. A. Fonseca et al. [Phys. Stat. Sol. (b)186, K57 (1994)] is incorrect.