Influence of a polaron dispersion and excitonic effect on a   magnetopolaron energy spectrum in a quantum well
  It has been shown, that a magnetopolaron discrete energy spectrum is realized in the optical experiments where exciting light is directed perpendicularly to a quantum well (QW) plane. The phonon dispersion as well as Coulomb attraction can only shift the magnetopolaron discrete energy levels and broad some of them. 
L.I. Korovin, I.G.Lang and S.T.Pavlov