New long-lived polarons in InAs/GaAs self-assembled quantum dots

We have investigated, by FIR magnetotransmission experiments up to 28 Tesla, the coupling between the electrons and the LO phonons in self-assembled InAs/GaAs quantum dots. The ground and the first excited states are s-like and p-like respectively, because of the Zeeman splitting of the p-state, two transitions s-p(+) and s-p(-) can be excited. The experiments consist of monitoring, by means of the magnetic field, a resonant interaction between the discrete (p(+/-), 0 LO-phonon) states and the continuum of either (s, 1 LO-phonon), (p(-), 1 LO-phonon) or (s, 2 LO-phonons). The magnetic field dispersion of the transmission minima shows huge deviations from the expected dispersion neglecting the electron-phonon interaction corresponding to the formation of I or 2 LO-phonons polarons. We have calculated the coupling between the relevant mixed electron lattice states using the Frohlich hamiltonian. An excellent agreement between the experiments and the calculations is obtained showing that the electron-LO phonon interaction in quantum dots does not correspond to a weak coupling behaviour, but that a strong coupling regime is observed with the formation of everlasting polarons.