Semiconducting transition metal dichalcogenides exhibit extraordinarily strong light matter and Coulomb interactions giving rise to the formation of tightly bound exciton states in the monolayer limit. Of particular interest is the continuously tunable coupling of excitons with free charge carriers that has been broadly explored for the exciton ground state so far. Here, we experimentally demonstrate dressing of the excited exciton states by a Fermi sea of free charge carriers in an electrically contacted hBN-encapsulated monolayer WSe₂ [1]. We identify excited state trions (Fermi polarons) in both n- and p-doped regimes, determining their binding energies in the zero-density limit. At elevated densities we demonstrate a highly efficient redistribution of the oscillator strengths, and provide evidence for autoionization, a process, commonly associated with intrinsically metastable, excited states in atomic systems, which inherently limits the lifetime of excited state trions in monolayer semiconductors.

[1] K. Wagner et al.: arXiv:2007.05396 (2020)