Supercondutividade mediada por excitons e exciton-polaritons em heteroestruturas bidimensionais

Abstract

This work aims to investigate superconductivity in two-dimensional semiconductor heterostructures. In these systems, electron excitation in the semiconductor, by electric fields or cavity photons, can give rise to bosonic quasiparticles known as excitons and exciton-polaritons. We study their feasibility as mediators of superconductivity in a two-dimensional electron gas. Within the context of BCS theory, we show that the interaction between them and conduction electrons gives rise to an effective attractive interaction between electrons favoring the formation of Cooper pairs, analogously to the phonon-mediated effective interaction mechanism in metals. In the literature, systems of this type are candidates for achieving high-temperature superconductivity due to their low effective mass and strong interaction. We begin with a brief introduction to superconductivity and BCS theory, where the alternative exciton-mediated mechanism is discussed. We proceed with a detailed description of the heterostructure under investigation. A theoretical model and a Hamiltonian are proposed, and it is shown that there exists an effective attractive interaction between electrons enabling superconductivity. The model is applied to both excitons and exciton-polaritons. We describe two algorithms to calculate the critical temperature TC and the superconducting gap ∆; thus, we show that there is a direct relationship between the increase in TC and the density of excitons/exciton-polaritons. The model also predicts a decrease in the critical temperature when the electron density Ne is increased. We conclude with an application to a van der Waals heterostructure composed of two transition metal dichalcogenides and a bilayer graphene (BLG) to host the electron gas. The heterostructure has the configuration WSe2-hBN-MoSe2-hBN-BLG, which is justified by the fact that condensed excitons have been recently experimentally detected at temperatures of the order of 100 K in this combination of materials. We show that for this system a critical temperature of ≈ 101.2 K is expected, placing it alongside high-temperature superconductors, such as Cuprates.