Using polarized twisted light to tailor the superposition of finite-momentum valley exciton states in transition-metal dichalcogenide monolayers*

A twisted light is a spatially structured light that carries a new degree of freedom of quantized orbital angular momenta (OAM), which, in addition to that of intrinsic spin angular momentum (SAM), i.e., polarization, is appealing for new quantum information technology. In this talk, we will present a theoretical study of the photo-excitation of valley excitons in transition-metal dichalcogenide monolayers (TMD-ML's) by using polarized Laguerre-Gaussian beams, one of the best-known twisted light's (TL's). Our studies show that the photoexcitation of polarized TL incident to a TMD-ML leads to the formation of the superposition of finite-momentum exciton (SFME) states, forming an exciton wave packet whose geometric pattern over the momentum and real spaces are encoded by the optical OAM. Furthermore, the momentum-dependent optical matrix element (MD-OME) of the SFME states for the exchange-split longitudinal and transverse exciton bands of TMD-ML's under TL excitation are shown to be highly directional and dependent on the polarization of the applied TL. The MD-OME's of the SFME states under the linearly polarized TL excitation mimic an exciton multiplexer allowing for selectively detecting the optical signatures of the meV-split longitudinal and transverse exciton bands of TMD-ML's.