Modification of Fano resonances by resonant polaron coupling in bulk GaAs

Strong modifications of the magneto-excitonic Fano lineshapes have been observed in the photoluminescence-excitation spectra of bulk GaAs when the energies of the transitions are tuned by an external magnetic field. We identify the origin of these changes as resonant polaronic coupling between the electrons or holes, forming the excitons, with longitudinal-optical phonons, in conduction and valence bands respectively. The resonant polaron effect alters the magneto-excitonic discrete states, destroying the quantum interferences responsible for the Fano asymmetry.