Polaritons in an Electron Gas—Quasiparticles and Landau Effective Interactions

Abstract

Two-dimensional semiconductors inside optical microcavities have emerged as a versatile platform to explore new hybrid light–matter quantum states. A strong light–matter coupling leads to the formation of exciton-polaritons, which in turn interact with the surrounding electron gas to form quasiparticles called polaron-polaritons. Here, we develop a general microscopic framework to calculate the properties of these quasiparticles, such as their energy and the interactions between them. From this, we give microscopic expressions for the parameters entering a Landau theory for the polaron-polaritons, which offers a simple yet powerful way to describe such interacting light–matter many-body systems. As an example of the application of our framework, we then use the ladder approximation to explore the properties of the polaron-polaritons. Furthermore, we show that they can be measured in a non-demolition way via the light transmission/reflection spectrum of the system. Finally, we demonstrate that the Landau effective interaction mediated by electron-hole excitations is attractive leading to red shifts of the polaron-polaritons. Our work provides a systematic framework to study exciton-polaritons in electronically doped two-dimensional materials such as novel van der Waals heterostructures.

Strongly Interacting Bose Polarons in Two-Dimensional Atomic Gases and Quantum Fluids of Polaritons

“…In semiconductor microcavities, new classes of polarons may arise, where the role of the polaron is played by an individual optical excitation dressed by its bath. These aforementioned polarons have received attention allowing for the development of polaron-based lasers [62] and the study of polaritonpolariton interactions [63][64][65][66]. The polaron-polariton, a quasiparticle resulting from the dressing of a polariton by its surroundings, has been experimentally realised in the context of the Fermi [67] and Bose polaron-polariton [61].…”

Cavity induced collective behavior in the polaritonic ground state

“…For instance, it is expected that the presence of twobody inter-component coupling will facilitate the generation of mediated interactions between the polariton quasiparticles of the different components [31]. These polariton-polariton interactions [128,129] will introduce polariton non-linearities [130] which could potentially lead to polariton condensation [131]. Finally, polariton-polariton interactions can also emerge, even for a single component system, e.g.…”

Repulsive Fermi and Bose Polarons in Quantum Gases

“…This has recently stimulated much cross-fertilization between the two fields (see, e.g., Ref. [32] in this Special Issue). In addition, the original polaron scenario of a single electron interacting with phonons in a crystal [7] has now been extended to quantum impurities immersed in a Bose-Einstein condensate-the so-called Bose polaron [33][34][35][36][37].…”