WSSe Monolayers as a New Darkish Material

Monolayers of transition metal dichalcogenides (TMD) are direct bandgap semiconductors in which optical and spin properties are dominated by the formation of bound electron-hole pairs, excitons. Alloys of TDMS have emerged as materials with tunable electronic structures, effective masses of carriers, and valley polarization with various alloy compositions. In this work we investigate the low-temperature photoluminescence spectra of WSSe monolayer embedded in hexagonal boron nitride (hBN) layers using external magnetic fields. On this basis we extract g-factors which help us to distinguish excitonic complexes. Additionally, we study PL spectra in the function of laser power and temperature. Based on these experiments we identify emissions due to bright (exciton and trion) transitions and dark (negative trion) transition. WSSe is comparable to WS2 and WSe2 so-called „darkish” materials, in which the excitonic ground state is optically inactive. The energy range of emission lines which correspond to excitionic complexes apparent in WSSe is similar to WS2 and WSe2. These two materials are known for their excellent valley polarisation due to the strong spin−orbit coupling and WSSe is expected to be the same.