Strongly correlated exciton-polarons in twisted homo-bilayer heterostructures

TL;DR

This paper investigates how excitons interact with strongly correlated electrons in twisted bilayer heterostructures, revealing unique spectral features that signal electronic correlation effects and phase transitions.

Contribution

It introduces the concept of exciton-polarons as probes for electronic correlations and demonstrates their spectral signatures across different correlated phases.

Findings

Double-peak structure in the repulsive polaron branch at non-integer fillings

Spectral discontinuity indicating phase transitions

Exciton-polarons serve as signatures of correlation-driven insulators

Abstract

We consider dressing of excitonic properties by strongly correlated electrons in gate controlled twisted homo-bilayer heterostructures. The combined effect of the moir\'e potential and the Coulomb interaction supports the formation of different strongly correlated phases depending on the filling, including charge-ordered metals or incompressible insulators at integer occupation. The coupling between excitons and electrons results in a splitting of the excitonic resonance into an attractive and a repulsive polaron peak. Analyzing the properties of the exciton-polarons across the different phases of the system, we reveal a discontinuous evolution of the spectrum with the formation of a double-peak structure in the repulsive polaron branch. The double-peak structure emerges for non-integer fillings and it is controlled by the energy separation between the quasi-particle states close to the Fermi level and the high-energy doublons excitations. Our results demonstrate that exciton-polarons carry a clear hallmark of the electronic correlations and, thus, provide a direct signature of the formation of correlation driven insulators in gate controlled heterostructures.