Electrical Control over Phonon Polarization in Strained Graphene

TL;DR

This paper demonstrates how uniaxial strain and electrostatic gating in graphene can be used to control phonon polarization, enabling tunable circular phonon modes with potential applications in phononics.

Contribution

It introduces a method to electrically control phonon polarization in strained graphene via magneto-phonon resonances and doping, a novel approach in phonon manipulation.

Findings

Achieved up to 40% circular phonon polarization.

Reversed phonon polarization sign by electron-hole doping.

Controlled phonon angular momentum using electrostatic fields.

Abstract

We explore the tunability of the phonon polarization in suspended uniaxially strained graphene by magneto-phonon resonances. The uniaxial strain lifts the degeneracy of the LO and TO phonons, yielding two cross-linearly polarized phonon modes and a splitting of the Raman G peak. We utilize the strong electron-phonon coupling in graphene and the off-resonant coupling to a magneto-phonon resonance to induce a gate-tunable circular phonon dichroism. This, together with the strain-induced splitting of the G peak, allows us to controllably tune the two linearly polarized G mode phonons into circular phonon modes. We are able to achieve a circular phonon polarization of up to 40 % purely by electrostatic fields and can reverse its sign by tuning from electron to hole doping. This provides unprecedented electrostatic control over the angular momentum of phonons, which paves the way toward phononic applications.