Two-phonon polaron resonances in self-assembled quantum dots

We study the second-order polaronic resonance between 2-LO-phonon states and p-shell electron states in a quantum dot. We show that the spectrum in the resonance area can be quantitatively reproduced by a theoretical model using only standard material constants, without any free parameters. We propose also a perturbative approach to the problem based on a quasi-degenerate perturbation theory. This method not only considerably reduces the numerical complexity without considerable loss of accuracy but also gives some insight into the structure and origin of the resonance spectrum.