Strongly enhanced exciton-phonon coupling in two-dimensional WSe2

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) (Gamma) phonon and A' exciton in WSe2 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 WSe2 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 WSe2/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 WSe2.