Advances in ab initio calculations of light-matter interaction in two-dimensional transition metal dichalcogenides

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit unusual electronic and optical properties. This talk will discuss novel first-principles calcns. of light absorption and emission in 2D-TMDs. First, we will show that visible light absorption per unit thickness in monolayer and few-layer TMDs is 1-2 orders of magnitudes greater than in conventional bulk semiconductors, and discuss application of TMDs to solar energy conversion. We will then introduce a formalism combining the ab initio Bethe-Salpeter equation with Fermi's golden rule to investigate light emission in 2DTMDs. We will show calcns. of the radiative lifetimes as a function of temp. in 2D-TMDs, which are in excellent agreement with expt. and provide new microscopic insights into exciton recombination in monolayers and heterobilayers. We will also address the anisotropic photoluminescence seen exptl. upon exciting TMDs with linearly polarized light. We generalize our radiative lifetime calcns. to obtain an equation for light emission as a function of angle and polarization, and show the presence of an inherently anisotropic photoluminescence due to the valley degeneracy of the lowest bright excitons. In closing, we will discuss our recent efforts on computing exciton-phonon interactions from first principles, and how these calcns. allow us to investigate nonequil. exciton dynamics in photoexcited 2D-TMDs.