Two-Dimensional Polaron-Polaritons: Interactions and Transport

Abstract

In this dissertation, we explore the interplay between strongly correlated electrons and optical polaritons confined to two dimensions. This is implemented experimentally with gallium arsenide quantum wells hosting a two-dimensional electron gas (2DEG). The structure is further embedded in an optical microcavity to reach the strong light-matter coupling regime. Optically created excitons in the quantum well act as impurities in the surrounding electron gas, forming collective excitations termed Fermi polarons. The resulting polaron-polariton modes are used to study the quantum Hall effect and allow tailoring photonic properties via control over the electrons. The electronic ground states in the integer and fractional quantum Hall regimes are investigated using polariton spectroscopy. This tool allows probing the spin polarization of the 2DEG by optical means. Many-body spin textures are studied around integer filling, in particular for the case of vanishing g-factor which is expected to favor large skyrmions. Using an optimized device structure, we advance polariton spectroscopy by drastically reducing unwanted modifications of the electron density upon optical illumination. We observe coupling of the polaron-polaritons to different fractional quantum Hall states as the filling factor is varied. In a second part, a polariton Hall bar device is fabricated to investigate the connection between electronic and polariton transport in two dimensions. We demonstrate acceleration of polaritons by shaping the electron density with external electric and magnetic fields. For a spin polarized electron gas, we demonstrate the creation of spin density gradients. They are used to route polaritons on the Hall bar device in a spin selective manner, reminiscent of an optical spin Hall effect. In the last part, we present four-wave mixing experiments performed with polaron-polaritons. The nonlinear optical response of polaritons is measured while they are coupled to different quantum Hall states. A surprising increase in nonlinear signal is found for the specific filling fractions 2/3 and 2/5. These results demonstrate enhanced polariton-polariton interactions both compared to other fillings and to the case of exciton-polaritons without 2DEG. This constitutes a step towards polariton blockade and suggests that nonlinear optics may allow us to extract properties of the correlated electronic states beyond linear spectroscopy.