Abstract
We investigate the interband transitions in several ensembles of
self-assembled InAs/GaAs quantum dots by using photoluminescence excitation
spectroscopy under strong magnetic field. Well defined resonances are observed
in the spectra. A strong anticrossing between two transitions is observed in
all samples, which cannot be accounted for by a purely excitonic model. The
coupling between the mixed exciton-LO phonon states is calculated using the
Fr\"{o}hlich Hamiltonian. The excitonic polaron energies as well as the
oscillator strengths of the interband transitions are determined. An
anticrossing is predicted when two exciton-LO phonon states have close enough
energies with phonon occupations which differ by one. A good agreement is found
between the calculations and the experimental data evidencing the existence of
excitonic polarons.