Ab Initio Radiative Lifetimes and Angular Dependence of the Photoluminescence in Two-Dimensional Transition Metal Dichalcogenides

We compute from first-principles the radiative lifetimes and the photoluminescence (PL) in two-dimensional (2D) transition metal dichalcogenides (TMDCs) with chemical formula MX2 (M=Mo, W and X=S, Se, Te). We first compute excitons in TMDC monolayers with the GW-Bethe Salpeter equation method. We then derive a new equation for the radiative lifetimes that extends a previous treatment [1] to correctly include the angular dependence of the PL. Besides refining the values of the temperature-dependent radiative lifetimes, our formalism can explain the angular dependence of the PL observed experimentally under linearly polarized light excitation, thus enabling ab initio computations of polar plots of the PL in excellent agreement with experiment. We further discuss how decoherence due to electron-phonon and electron-electron scattering modifies the angular dependence of the PL, and how non-parabolic exciton dispersions are expected to change the radiative lifetimes. Our work presents a direct connection between microscopic exciton states in TMDCs and PL measurements, thus providing computational tools to advance understanding of carrier and exciton dynamics in 2D-TMDCs.

[1] M. Palummo, M. Bernardi, and J. C. Grossman, Nano Letters 15, 2794 (2015)