Autoionization and dressing of excited excitons by free carriers in monolayer WSe2

Koloman Wagner, Edith Wietek, Jonas D. Ziegler, Marina Semina, Takashi Taniguchi, Kenji Watanabe, Jonas Zipfel, Mikhail M. Glazov, Alexey Chernikov

Published 2020-07-10Version 1

We experimentally demonstrate dressing of the excited exciton states by a continuously tunable Fermi sea of free charge carriers in a monolayer semiconductor. It represents an unusual scenario of two-particle excitations of charged excitons previously inaccessible in conventional material systems. We identify excited state trions, accurately determine their binding energies in the zero-density limit for both electron- and hole-doped regimes, and observe emerging many-body phenomena at elevated doping. Combining experiment and theory we gain access to the intra-exciton coupling facilitated by the interaction with free charge carriers. We provide evidence for a process of autoionization for quasiparticles, a unique scattering pathway available for excited states in atomic systems. Finally, we demonstrate a complete transfer of the optical transition strength from the excited excitons to dressed excitons, Fermi polarons, as well as the associated light emission from their non-equilibrium populations.