Impurity vibrations of copper defect complexes in gallium arsenide crystals

Dynamical properties of several copper defect complexes in GaAs are studied. The complexes studied include models for the C and F centers recently investigated experimentally by Gross, Safarov, Sedov, and Marushchak. It is shown that these models are capable of giving rise to resonance modes whose frequencies agree with the positions of peaks in the optical spectra of these defect complexes, when reasonable changes in the force constants coupling the substitutional copper impurities to the host crystal are included in the dynamical models. In addition the vibronic and infrared absorption spectra of these complexes have been calculated.     

Enhanced backscattering in a magnetic field

By infinite-order perturbation theory the authors study the scattering of p-polarized light from a small-amplitude random grating ruled on the surface of a metal or an n-type semiconductor to which a constant magnetic field is applied. The surface is defined by the equation x₃=ζ(x₁), where the surface profile function ζ(x₁) is a stationary, stochastic, Gaussian process. The plane of incidence is the x₁x₃ plane, and the magnetic field is directed along the x₂ axis. We find that the position of the peak in the angular distribution of the intensity of the incoherent component of the scattered light that is observed in the retroreflection direction in the absence of the magnetic field—enhanced backscattering—is shifted in the direction of larger scattering angles from the retroreflection direction with increasing magnetic field strength. At the same time the width of the peak increases and its amplitude decreases. This is interpreted as due to the breakdown of the coherency between the contribution to backscattering from a given light/surface polariton path and from its time-reversed partner, caused by the removal of time reversal symmetry from the scattering system by the application of the external magnetic field. The latter is manifested by the non-reciprocity of the surface polariton dispersion relation in the presence of the magnetic field.     

Enhanced backscattering and transmission of light from random surfaces on semi-infinite substrates and thin films

The enhanced backscattering of light from a random surface is manifested by a well defined peak in the retro-reflection direction in the angular distribution of the intensity of the incoherent component of the light scattered from such a surface. In this paper we present several new theoretical and experimental results bearing on the conditions under which enhanced backscattering occurs, and the way in which this phenomenon depends on the nature of the random surface roughness, both in the case that the random surface bounds a semi-infinite scattering medium and in the case that it bounds a film, either free-standing or on a reflecting substrate. In addition, we present new results on the transmission of light through thin metallic films bounded by random surfaces, which display the phenomenon of enhanced transmission, namely a well defined peak in the antispecular direction in the angular distribution of the intensity of the incoherent component of the light transmitted through such films.     

Theory of surface polaritons associated with the extreme anomalous skin effect in normal and superconducting metals

Surface polaritons associated with the extreme anomalous skin effect in metals have been theoretically investigated for the normal and superconducting states. The Pippard expression for the current density was used to obtain the nonlocal conductivity tensor for the extreme anomalous limit. From the resultant components of the dielectric tensor, the specular reflection-mirror image technique of Kliewer and Fuchs was used to obtain the surface polariton dispersion relation; calculations were performed for aluminium. For frequencies above the superconductor gap frequency but much less than the plasma frequency, the surface polariton behaviour is nearly the same for the normal and superconductor (T = 0 K) cases. For frequencies below the gap frequency, the surface polariton damping is zero for the superconductor case, and is nonzero and decreases rapidly with frequency for the normal conductor case.