Observing the Birth of Rydberg Exciton Fermi Polarons on a Moire Fermi Sea

TL;DR

This study directly observes the formation and evolution of Rydberg exciton Fermi polarons in a 2D heterostructure, revealing how many-body interactions influence quasiparticle properties in moire superlattices.

Contribution

It provides the first direct observation of Rydberg exciton Fermi polarons in a 2D heterostructure using pump-probe spectroscopy, linking exciton interactions with localized carriers.

Findings

Exciton Fermi polaron binding energy increases with carrier density.

The relaxation rate of exciton Fermi polarons depends on the electron or hole density.

Rydberg exciton interactions are significantly affected by the moire superlattice environment.

Abstract

The optical spectra of two-dimensional (2D) semiconductors are dominated by tightly bound excitons and trions. In the low doping limit, trions are often described as three-body quasiparticles consisting of two electrons and one hole or vice versa. However, trions are more rigorously understood as quasiparticles arising from the interaction between an exciton and excitation of the Fermi sea - referred to as exciton Fermi polaron. Here we employ pump-probe spectroscopy to directly observe the formation of exciton Fermi polarons in a model system composed of a WSe2 monolayer adjacent to twisted bilayer graphene (tBLG). Following the pump-injection of Rydberg excitons in WSe2, a time-delayed probe pulse tracks the development of Rydberg exciton Fermi polarons as interactions with localized carriers in the tBLG moire superlattice evolve. Both the exciton Fermi polaron relaxation rate and binding energy are found to increase with electron or hole density. Our findings provide insight into the optical response of fundamental excitations in 2D Van der Waals systems and reveal how many-body interactions give rise to emergent quasiparticles.