The role of the electron-phonon interaction for optical properties of van der Waals materials

The optical response of semiconductors is often strongly affected by electron-phonon interaction. An electron-phonon scattering rate, as obtained from Fermi’s golden rule, typically leads to a broadening of spectral lines, and polaronic renormalizations may lead to temperature-dependent spectral shifts. However, more pronounced effects on the spectra can occur if the phonon influence cannot be reduced to a Markovian scattering rate, i.e., if non-Markovian effects are becoming important. This is often the case when strongly localized electronic states are involved in the optical transitions.

In this talk I will exemplarily discuss the phonon influence on the optical response of two types of structures in van der Waals materials: defect centers in hexagonal boron nitride acting as single-photon emitters and twisted bilayers of transition metal dichalcogenides in an optical cavity giving rise to moiré exciton polaritons. We will see that the characteristic shapes of optical signals both in the time and the frequency domain provide valuable information on details of the phonon-induced decoherence and the optically induced phonon dynamics, which are important for possible applications in the fields of optoelectronics and quantum information technology.