Strongly enhanced exciton-phonon coupling in two-dimensional WSe2

Abstract

The recently emerging laminar transition metal dichalcogenides provide an unprecedented platform for exploring fascinating layer-dependent properties. Determining the dependence of exciton-phonon coupling (EPC) on dimensionality would set a foundation for these exotic thickness-dependent phenomena. Here we report the observation of layer-dependent EPC between the ${A}_{1g}(\mathrm{\ensuremath{\Gamma}})$ phonon and A\ensuremath{'} exciton in $\mathrm{WS}{\mathrm{e}}_{2}$ down to the monolayer limit. Our results uncover that the strength of EPC increases dramatically with a descent of layer thickness. Compared with their bulk counterparts, the strength of EPC in monolayer $\mathrm{WS}{\mathrm{e}}_{2}$ is enhanced by nearly an order of magnitude. Furthermore, our work demonstrates that the giant EPC in the monolayer plays a prominent role in the exotic interlayer EPC of $\mathrm{WS}{\mathrm{e}}_{2}$/boron nitride heterostructures. The gigantic EPC in the two-dimensional limit provides a firm basis for understanding and manipulating the peculiar phenomena and novel optoelectronic applications based on atomically thin $\mathrm{WS}{\mathrm{e}}_{2}$.