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

TL;DR

This paper explores how free charge carriers in monolayer WSe2 modify excited exciton states, revealing many-body phenomena, autoionization processes, and a transfer of optical transition strength to dressed excitons and Fermi polarons.

Contribution

It introduces the experimental observation of exciton dressing by a tunable Fermi sea and the autoionization process in monolayer WSe2, a novel scenario in 2D materials.

Findings

Identification of excited state trions and their binding energies.

Observation of many-body phenomena at elevated doping levels.

Evidence of autoionization and transfer of optical strength to dressed states.

Abstract

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.