Exchange and polaron corrections for excitons in the degenerate-band case

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Abstract
Corrections to the exciton energies due to exchange interaction and polar electron-phonon coupling are considered for the degenerate-band case. Mass renormalization and electron-hole interaction potentials induced by the Fröhlich coupling to longitudinal-optical phonons have been established in a previous paper by a tensor operator formalism. Here we present a formulation of the electron-hole exchange in the same theoretical concept. The screening of the exchange interaction is rediscussed. We conclude that the exchange term is screened by a background dielectric constant whose origin is the exchange coupling between all excited electronic states. On the basis of this theory exciton energies for cubic III-V, II-VI semiconductors and CuBr are computed and the influence of band degeneracy, polar electron-phonon coupling, and exchange interaction on the exciton states is discussed.