Abstract
We have placed a van der Waals homostructure, formed by stacking three two-dimensional layers of WS(2) separated by insulating hBN, similar to a multiple-quantum well structure, inside a microcavity, which facilitates the formation of quasiparticles known as exciton-polaritons. The polaritons are a combination of light and matter, allowing laser emission to be enhanced by nonlinear scattering, as seen in prior polariton lasers. In the experiments reported here, we have observed laser emission with an ultralow threshold. The threshold was approximately 59 nW/μm(2), with a lasing efficiency of 3.82%. These findings suggest a potential for efficient laser operations using such homostructures.