Radius-independent resonances in electron-hole drop magnetoplasmas

Abstract

We discuss theoretically the microwave and far-infrared spectra which exist in the parameter ranges appropriate to small electron-hole drops in Ge when they are located in a dc magnetic field. Our examination employs the perturbation-theory results of Ford, Furdyna, and Werner, which rigorously describe the interaction of a small gyrotropic sphere with external time-varying electric and magnetic fields. We consider only the two high-symmetry orientations of the dc magnetic field, parallel to the [100] axis of Ge and parallel to the [111] axis of Ge, for which the electron-hole magnetoplasma in Ge is described by a dielectric tensor of a form amenable to the perturbation theory. The theory predicts several radius-independent electric and magnetic resonances. In parameter ranges appropriate to compensated electron-hole drops in Ge, we find that the positions of all resonances are functions only of the various carrier effective masses and ratios of the concentrations of the different carriers. The intensities of the electric resonances are inversely proportional to the electron carrier concentration and vary as the cube of sphere radius and the fourth power of frequency. The intensities of the magnetic resonances are directly proportional to the electron carrier concentration and vary with the fifth power of radius and the square of frequency. We find that two additional electric resonances can occur when the electron-hold drop is uncompensated. The positions of these resonances depend directly upon the difference in the electron and hole carrier densities.