Charge density excitations of two-dimensional magnetoplasma in semiconductor superlattices

Abstract

This paper presents the theoretical investigation of collective charge density excitations in two-dimensional semiconductor superlattices subjected to a perpendicular magnetic field. We use a simple electromagnetic theory with a two-dimensional Dirac-δ function for the charge density profile. The magnetoplasmon dispersion relations are derived for an infinite and semi-infinite superlattices, both type II (InAs-GaSb systems) and type I (GaAs-AlxGa1−xAs systems). We emphasize on the magnetoplasma polaritons of semi-infinite superlattices. A detailed analytical diagnosis has been made of the dispersion relations to study the various limiting situations. The surface charge density excitations in the type II superlattices display a broken degeneracy in the retarded limit due to the presence of an applied magnetic field. This interestingly happens with the surface plasmon branch lying within the gap between two bulk bands. Moreover, the Q (Bloch wave vector)=0 edge of the bulk bands exhibits the splitting of the dispersion curve at a frequency (ω) greater than the cyclotron frequency (ωc). Application of a magnetic field results, in general, in pushing the whole spectrum lying above ω=ωc. The numerical results, including the retardation effects, both for zero and nonzero magnetic fields, have been presented for several illustrative cases.