Polaron states in InAs/GaAs quantum dots: strong electron–phonon coupling regime

Abstract

We report on the magneto-optical evidence and theoretical modelling of polaron effects in self-assembled InAs/GaAs quantum dots. Using far-infrared magneto-transmission experiments performed up to 28 T at T=2 K in doped QDs samples, we investigate the electronic transitions between the ground and first excited states. We observe very large anticrossings in the B-dispersion of the magneto-optical transitions, whose existence cannot be explained by a purely electronic model. We thus calculate the coupling between the mixed electron-lattice states using the Fröhlich Hamiltonian and determine the polaron states and the energies of the dipolar electric transitions. An excellent agreement between the calculations and the experimental data is obtained, demonstrating that the magneto-optical transitions occur between polaron states. The time dependence of the survival probability is calculated for the various non-interacting electron–phonon states. Such probabilities are found to oscillate and do not show an exponential decay as it would be the case for a weak coupling regime. This last argument confirms that the electrons and the LO-phonons experience a strong coupling regime in QDs.