A Tunable Phonon-Exciton Fano System in Bilayer Graphene

TL;DR

This paper reports a tunable Fano resonance system in bilayer graphene where hybrid phonon-exciton states can be controlled electrically, revealing new quantum interference effects and potential phonon laser applications.

Contribution

It introduces a novel many-body Fano system in bilayer graphene with electrically tunable phonon-exciton interactions and Fano resonance characteristics.

Findings

Observation of characteristic Fano lineshapes in infrared absorption.

Electrical gating allows continuous tuning of the Fano resonance.

Potential for phonon laser development through population inversion.

Abstract

Interference between different possible paths lies at the heart of quantum physics. Such interference between coupled discrete and continuum states of a system can profoundly change its interaction with light as seen in Fano resonance. Here we present a unique many-body Fano system composed of a discrete phonon vibration and continuous electron-hole pair transitions in bilayer graphene. Mediated by the electron-phonon interactions, the excited state is described by new quanta of elementary excitations of hybrid phonon-exciton nature. Infrared absorption of the hybrid states exhibit characteristic Fano lineshapes with parameters renormalized by many-body interactions. Remarkably, the Fano resonance in bilayer graphene is continuously tunable through electrical gating. Further control of the phonon-exciton coupling may be achieved with an optical field exploiting the excited state infrared activity. This tunable phonon-exciton system also offers the intriguing possibility of a 'phonon laser' with stimulated phonon amplification generated by population inversion of band-edge electrons.