Phonon excitation and instabilities in biased graphene nanoconstrictions

TL;DR

This study investigates how high current densities induce phonon instabilities in graphene nanoconstrictions, revealing nonlinear heating effects and potential limitations on their current-carrying capacity.

Contribution

It provides first-principles analysis of current-induced phonon behavior and breakdown mechanisms in graphene nanoconstrictions under high bias conditions.

Findings

Nonlinear Joule-heating near electronic resonances

Breakdown of harmonic approximation due to negatively damped phonons

Potential stability limits for high-current graphene devices

Abstract

We calculate the phonons in a graphene nanoconstriction(GNC) in the presence of a high current density. The Joule-heating, current-induced forces, and coupling to electrode phonons is evaluated using first principles nonequilibrium DFT-NEGF calculations. Close to a resonance in the electronic structure we observe a strongly nonlinear heating with bias and breakdown of the harmonic approximation. This behavior results from negatively damped phonons driven by the current. The effect may limit the stability and capacity of graphene nanoconstrictions to carry high currents.