Theory of the absorption lineshape in monolayers of transition metal dichalcogenides

Monolayers of transition metal dichalcogenides are attractive materials for optoelectronics due to their strong exciton-light interaction. At the same time exciton-phonon interaction is exceptionally strong in these materials which is visible in optical spectra. In this contribution we compare different theoretical methods for the description of linear absorption spectra in 2D semiconductors [1]. To be specific, we consider the spectra of MoSe2 using either a correlation expansion in 2nd or 4th Born Approximation (2BA or 4BA) or a time convolutionless master equation (TCL). Additionally we introduce a damped version of the 4th Born Approximation (4BA-D) partially accounting for contributions of even higher-order correlations. We find that the 2nd Born Approximation gives poor results for elevated temperatures due to the strong exciton-phonon interaction such that higher-order methods are necessary (4BA and 4BA-D). Surprisingly, the TCL provides very good results despite its simplicity when compared to higher-order correlation expansion. We show that the TCL is very accurate and allows for an easy interpretation of the underlying non-Markovian effects.