Optical coherence in atomic monolayer transition metal dichalcogenides limited by electron-phonon interactions*

We systematically investigate the excitonic dephasing of three representative transition metal dichalcogenides, namely MoS$_{\mathrm{2}}$, MoSe$_{\mathrm{2}}$ and WSe$_{\mathrm{2}}$ atomic monolayer thick and bulk crystals, in order to gain proper understanding of the factors that determine the optical coherence in these materials. Coherent nonlinear optical spectroscopy, temperature dependent absorption combined with `ab initio' theoretical calculations of the phonon spectra, indicate electron-phonon interactions to be the limiting factor.