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 excitations of the Fermi sea—referred to as exciton Fermi polarons. 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 moiré superlattice evolve. Both the exciton Fermi polaron relaxation rate and the 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.

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 excitations of the Fermi sea—referred to as exciton Fermi polarons. 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 moiré superlattice evolve. Both the exciton Fermi polaron relaxation rate and the 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.

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 excitations of the Fermi sea—referred to as exciton Fermi polarons. 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 moiré superlattice evolve. Both the exciton Fermi polaron relaxation rate and the 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.

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 excitations of the Fermi sea—referred to as exciton Fermi polarons. 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 moiré superlattice evolve. Both the exciton Fermi polaron relaxation rate and the 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.