Exciton Mott Transition in Two-Dimensional Semiconductors

Abstract: Exciton many-body interaction bear great implication for application in advanced photonic devices and quantum science and technology such as quantum computing, but the fundamental understanding about exciton many-body interaction is very limited. Here we provide numerous new insights into the fundamentals of exciton Mott transition (EMT), a manifestation of exciton many-body interaction evidenced by the ionization of excitons into a plasma of unbound electrons and holes, i.e. electron-hole plasma (EHP), by taking advantage of the unique properties of two-dimensional (2D) semiconductors like monolayer MoS2. We clarify long-standing controversies on the continuousness and criteria of EMT, quantify the charge carrier distribution among the co-existing exciton and EHP phases, establish correlation between the emission features and charge densities of EHP, and elucidate the physical state of EHP charge carriers as nanoscale electron-hole complex rather than individually free charges. These results lay down a foundation for furthering the studies of exciton many-body interaction and also for utilizing the interaction in quantum science/technology and the development of advanced optoelectronic devices.