Electron-hole plasma formation dynamics observed through exciton-plasma interactions in transition metal dichalcogenides

How do the many-particle interactions evolve in semiconductors is crucial for understanding light-matter interactions. We observe Coulomb-correlated electron-hole plasma formation via its interaction with excitons in a transition metal dichalcogenide semiconductor. We observe that under intense photoexcitation $\ensuremath{\sim}{10}¹⁹$ per ${\mathrm{cm}}³$, huge damping destroys the Coulomb correlation and hinders the plasma formation until a majority of the free carriers recombine and the plasma oscillation period becomes sufficiently smaller than the damping time constant. Moreover, only 1%--3% of the injected free carriers form Coulomb-correlated plasma. Our study sheds light on exciton-plasma interactions and quasistatic Coulomb screening, which play pivotal roles in device engineering.