Resonant Brillouin scattering in CuBr

We have studied the dispersion of polaritons in CuBr by means of resonant Brillouin scattering. As a result of $k$-linear terms and exchange coupling the polariton dispersion relations are highly structured. From a theoretical fit we have derived the pertinent exciton parameters and from them the corresponding Luttinger band parameters. The scattering mechanisms invoked for the interpretation of the experiments are piezoelectric scattering and deformation potential scattering. On the basis of independently determined deformation-potential constants it is shown that the deformation-potential scattering suffices to account for the observed scattering efficiencies in piezoelectric forbidden cases. From an analysis of the scattering intensities it is possible, in principle, to determine independently the absolute deformation potentials of the conduction and the valence bands.