Switching of K-Q intervalley trions fine structure and their dynamics in n-doped monolayer WS2

Monolayer group VI transition metal dichalcogenides (TMDs) have recently emerged as promising candidates for photon-ic and opto-valleytronic applications. The optoelectronic properties of these atomically-thin semiconducting crystals are strongly governed by the tightly bound electron-hole pairs such as excitons and trions (charged excitons). The anomal-ous spin and valley configurations at the conduction band edges in monolayer WS2 give rise to even more fascinating valley many-body complexes. Here we find that the indirect Q valley in the first Brillouin zone of monolayer WS2 plays a critical role in the formation of a new excitonic state, which has not been well studied. By employing a high-quality h-BN encapsulated WS2 field-effect transistor, we are able to switch the electron concentration within K-Q valleys at conduc-tion band edges. Consequently, a distinct emission feature could be excited at the high electron doping region. Such fea-ture has a competing population with the K valley trion, and experiences nonlinear power-law response and lifetime dy-namics under doping. Our findings open up a new avenue for the study of valley many-body physics and quantum optics in semiconducting 2D materials, as well as provide a promising way of valley manipulation for next-generation entangled photonic devices.