Catastrophic Ionization in Monolayer Transition Metal Dichalcogenides

Recent observations in monolayer transition metal dichalcogenides (TMDs) demonstrate that a high density exciton gas undergoes a Mott transition into an electron-hole plasma (EHP), which through the correlation and exchange interaction, condenses into a macroscopic liquid state, or electron-hole liquid. This astonishing many-body interaction is facilitated by band-gap renormalization (BGR), which effectively lowers the band-gap in TMDs and reduces the exciton binding energy in the presence of high charge density. Utilization of this phenomena allows initial low-intensity excitations to instigate a runaway process, where further BGR facilitates a catastrophic ionizing event. During this transition, a low-density exciton gas completely ionizes into an EHP with only a 2.5% increase in power density, yielding a greater than 100-fold increase in luminescence yield. The drastic change in luminescence and charge density resulting from catastrophic ionization makes TMDs a promising material for high charge density, switchable opto-electronic devices.