Retardation effects and transverse collective excitations in semiconductor superlattices

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Abstract
In this paper we examine the transverse collective modes in type-I and -II semiconductor superlattices which are associated with retardation effects. We use a simple model of the electronic structure to obtain the current response to an external perturbation. The zeros of the response function yield the dispersion relations of the collective modes of the system. In addition to the usual modes, which have been discussed elsewhere, we find the existence of helicons, plasmon-helicons, and Alfvén waves. The helicons have interesting propagation characteristics which may be useful for measurements of the quantum Hall effect.