Volume 23, Issue 1, January 1997
Index of content:
23(1997); http://dx.doi.org/10.1063/1.593414View Description Hide Description
23(1997); http://dx.doi.org/10.1063/1.593334View Description Hide Description
The results of experimental investigations of diffusion processes in solid helium are reviewed. It is shown that impurities in hcp are narrow-band quasiparticles whose motion can be adequately described in the existing theory of quantum diffusion. The observed peculiarities of diffusion in the bcc phase of concentrated –solutions, i.e., a noticeable diffusive transport at concentrations higher than critical, the independence of the diffusion coefficient on the concentration for an abrupt increase in for and a dependence of on the diffusion length in the latter case, have not received a quantitative interpretation. The relation between diffusion phenomena in concentrated solutions and the percolation problem is emphasized. The results of experiments on vacancydiffusion are analyzed, and it is proved that vacancies in – are wide-band quasiparticles.
23(1997); http://dx.doi.org/10.1063/1.593330View Description Hide Description
This paper presents a brief review of the electron properties in two-dimensional systems which contain zero-range scatterers which are subjected to a magnetic field. The electron spectrum is described for a periodic arrangement of point scatterers and rational magnetic flux per unit cell. Delocalized states on the Landau levels are constructed for the case of positional disorder. The electron localization in a one-dimensional disordered set of scatterers is studied. Application to the study of electron transmission through quantum dots and ballistic channels is reviewed.
23(1997); http://dx.doi.org/10.1063/1.593331View Description Hide Description
An algorithm for calculating the surface impedance of a normal isotropic metal is constructed by taking into account the arriving term in the collision integral (in the case of specular reflection). Analytic expressions are obtained for scattering probability describing the -, -, and -scattering.
23(1997); http://dx.doi.org/10.1063/1.593332View Description Hide Description
The dependence of the resistance of a layered conductor with an arbitrary quasi-two-dimensional electron energy spectrum on the magnitude and orientation of a magnetic field relative to the layers is analyzed. It is shown that, when the current flows along the normal to the layers, the resistance of the sample depends significantly on the angle between the normal and the strong magnetic field vector; for the resistance increases linearly with the magnetic field in a wide range of magnetic fields.
23(1997); http://dx.doi.org/10.1063/1.593333View Description Hide Description
The surface magnetization of metals associated with electrons whose orbits are tangential to the metal boundary is investigated, taking into account anisotropy in the energy spectrum of conduction electrons. It is shown that the angular dependence of magnetization has peculiarities determined by the curvature of the Fermi surface at the reference points. Explicit expressions have been obtained for the surfacemagnetic susceptibility of electrons in bismuth, and appropriate numerical estimates of its value have been made.
23(1997); http://dx.doi.org/10.1063/1.593335View Description Hide Description
A mathematical method based on a reduced representation of the electron–electron collision operator acting in the space of quasi-equilibrium functions is constructed. A number of kinetic phenomena such as the evolution of highly anisotropic and high-energy electron distributions, the quasi-hydrodynamic effect in electrical conduction, and a new nonlinear transport mode are described from a unified point of view. Kinetic effects which can be observed in experiments on electron beam propagation and electrical conduction of (GaAs)Al wires with a high mobility of charge carriers are predicted.
The high-frequency conductivity tensor of a two-dimensional electron gas with electron impurity states in a magnetic field23(1997); http://dx.doi.org/10.1063/1.593336View Description Hide Description
The Lifshits method of local perturbations is used for studying the properties of a two-dimensional electron-impurity system in a quantizing magnetic field perpendicular to the plane of electron motion. The high-frequency conductivity tensor of the system is calculated in the model of independent point impurity atoms, taking into account the impurity states of electrons and spatial dispersion. The dissipative component of the conductivity has narrow resonant peaks at frequencies of electron transitions between the Landau levels and local levels, which are induced by the magnetic field. In zero magnetic field, these peaks merge into one broad peak lying above the threshold frequency for electron transitions from a local level to the energy band. Numerical values of the peak heights are obtained for semiconducting structures with a two-dimensional electron gas.
23(1997); http://dx.doi.org/10.1063/1.593337View Description Hide Description
The theory of finite-dimensional perturbations of self-adjoint operators, which is aimed at the solution of physical problems, is reviewed. Special attention is paid to the special kind of operators, which permits efficient application of the J-matrix technique. The spectral density of a periodic J-matrix is calculated.
23(1997); http://dx.doi.org/10.1063/1.593338View Description Hide Description
The waves localized near the free surface (001) of a fcc crystal and propagating along the  direction are analyzed in the model of central interaction of nearest neighbors. The frequencies of these waves fall in the gaps of the frequency spectrum of bulk harmonic vibrations for a fixed value of the wave vector along the surface. The long-wave limit and the case of wave vectors close to the Brillouin zone boundary are studied analytically. These limiting dependences are in accord with the results obtained earlier by other authors by numerical methods. The analytical calculations in the limiting intervals of vector are supplemented with numerical calculations for arbitrary values of wave vectors. It is significant that the waves under investigation have a displacement component perpendicular to the crystal surface and hence can be studied by standard methods of inelastic scattering of helium atoms.
23(1997); http://dx.doi.org/10.1063/1.593339View Description Hide Description
The general system of equations describing the smoothing of surface structure in solids under irradiation is formulated. It is shown that under real conditions the system can be reduced to a simpler form which has an exact solution. A general formula describing the smoothing of surface structure with time is derived. As a special case, this formula gives the evolution (smoothing) of the relief in the absence of radiation, which is associated with the difference in curvatures for different roughnesses. The physical reason behind the intensification of smoothing under irradiation is the difference between the positions of the centers of gravities for concentration profiles of vacancies and interstitials. The radiation gives rise to a new type of dependence of the rate of smoothing on the roughness parameters of the surface, which permits the experimental separation of the contribution from radiation to smoothing and simultaneously makes it possible to determine some parameters which are difficult to measure.
23(1997); http://dx.doi.org/10.1063/1.593340View Description Hide Description
New classes of exact solutions of the Schrödinger equation with simple explicit analytic expressions for potential fields, energy levels, and wave functions of stationary states are considered. The solutions are discovered with the help of new original methods elaborated in the quantum theory of spin systems. The corresponding effective potentials are compared to similar models of soliton origin. The main attention is paid to peculiar phenomena such as quasi-exact solvability, potentials with multiple and flexible profiles, fourth-order extrema, finite-band spectra and structural transformations in energy bands, and the spin–soliton analogy.
23(1997); http://dx.doi.org/10.1063/1.593341View Description Hide Description
The Hamiltonian description of the motion of arbitrary discontinuity surfaces is proposed on the basis of the variational principle, taking into account the conservation laws in terms of consecutively introduced volume potentials (of the Clebsch type) as constraints. Such a method of introduction of Hamiltonian variables makes it possible to generalize the known canonical variables for the interface between two media to the cases of shock waves and slip surfaces. The results are compared with the introduction of surface Hamiltonian variables through the canonical transformations of bulk Hamiltonian variables. The results permit a direct generalization to the case of magnetohydrodynamics, plasmas, superfluidliquids, and other media for which the bulk Hamiltonian equations are known.