Phonons in Quantum Dots and Their Role in Exciton Dephasing

Abstract

The acoustic phonon spectrum is significantly modified for embedded quantum dots by inhomogeneous change of material properties and intrinsic strain. The change of the local elastic properties due to strain is calculated employing density functional theory and used as input for phonon calculations within continuum elasticity model. It is demonstrated that overall the exciton–phonon coupling strength is reduced, characteristic oscillations appear in the excitonic polarization, and the spectral broadband is modified compared to a bulk phonon assumption. The zero phonon line broadening is discussed in terms of real and virtual phonon-assisted transitions between different exciton levels in a quantum dot. A microscopic theory of the excitonic multilevel system coupled to acoustic phonons is developed, and the full time-dependent polarization and absorption are calculated using the cumulant expansion. Examples are given for dephasing of optical excitations in single and vertically coupled quantum dots.