Strongly Coupled Exciton--Hyperbolic-phonon-polariton Hybridized States in hBN-encapsulated Biased Bilayer Graphene

TL;DR

This paper demonstrates the formation of strongly coupled hybridized exciton-HPhP states in hBN-encapsulated biased bilayer graphene, revealing tunable light-matter interactions in the mid-infrared spectrum through electromagnetic modeling.

Contribution

It introduces a new tunable platform for engineering strongly coupled quasiparticle states in biased graphene systems using hBN encapsulation and electromagnetic modeling.

Findings

Strong exciton-HPhP hybridization observed in MIR spectrum

Hybridized states are highly tunable via system symmetry

Derived dispersion relations show controllable hybridization effects

Abstract

Excitons in biased bilayer graphene are electrically tunable optical excitations residing in the mid-infrared (MIR) spectral range, where intrinsic optical transitions are typically scarce. Such a tunable material system with an excitonic response offer a rare platform for exploring light-matter interactions and optical hybridization of quasiparticles residing in the long wavelength spectrum. In this work, we demonstrate that when the bilayer is encapsulated in hexagonal-boron-nitride (hBN)-a material supporting optical phonons and hyperbolic-phonon-polaritons (HPhPs) in the MIR-the excitons can be tuned into resonance with the HPhP modes. We find that the overlap in energy and momentum of the two MIR quasiparticles facilitate the formation of multiple strongly coupled hybridized exciton-HPhP states. Using an electromagnetic transmission line model, we derive the dispersion relations of the hybridized states and show that they are highly affected and can be manipulated by the symmetry of the system, determining the hybridization selection rules. Our results establish a general tunable MIR platform for engineering strongly coupled quasiparticle states in biased graphene systems, opening new directions for studying and controlling light-matter interactions in the long-wavelength regime.