Collective electronic excitation in a trapped ensemble of photogenerated dipolar excitons and free holes revealed by inelastic light scattering

TL;DR

This study reveals a sharp collective plasmon mode in a dense, trapped ensemble of photogenerated dipolar excitons and free holes in GaAs quantum wells, demonstrating the potential to explore many-body physics in such systems.

Contribution

It introduces a combined emission and inelastic light scattering approach to identify collective excitations in trapped excitonic systems with free holes.

Findings

Identification of a sharp collective mode at 0.44 meV

Coupling of plasmon excitation to indirect excitons

Quantum-confined Stark effect unaffected by free carriers

Abstract

Photogenerated excitonic ensembles confined in coupled GaAs quantum wells are probed by a complementary approach of emission spectroscopy and resonant inelastic light scattering. Lateral electrostatic trap geometries are used to create dense systems of spatially indirect excitons and excess holes with similar densities in the order of 10$^{11}$ cm$^{-2}$. Inelastic light scattering spectra reveal a very sharp low-lying collective mode that is identified at an energy of 0.44 meV and a FWHM of only ~50 $\mu$eV. This mode is interpreted as a plasmon excitation of the excess hole system coupled to the photogenerated indirect excitons. The emission energy of the indirect excitons shifts under the application of a perpendicular applied electric field with the quantum-confined Stark effect unperturbed from the presence of free charge carriers. Our results illustrate the potential of studying low-lying collective excitations in photogenerated exciton systems to explore the many-body phase diagram, related phase transitions, and interaction physics.