Anharmonicity of the acoustic modes of graphene

TL;DR

This study investigates the anharmonic behavior of graphene's acoustic phonons at finite temperature using a non-perturbative harmonic linear response method, highlighting the effects of stress and temperature.

Contribution

It introduces a harmonic linear response approach to analyze anharmonic phonon shifts in graphene, comparing results with analytical models and emphasizing stress effects.

Findings

Better agreement with perturbation theory than previous models

Stress influences on phonon anharmonicity are quantified

Temperature and zero-point vibrations affect out-of-plane shifts

Abstract

The anharmonicity of the acoustic phonon dispersion of graphene has been studied by the harmonic linear response (HLR) approach at finite temperature. This is a non-perturbative method based on the linear response of the system to applied forces, as derived from equilibrium computer simulations. Anharmonic shifts are analyzed in the long-wavelength limit at room temperature, with emphasis in the effect of applied tensile or compressive in-plane stress. The simulation results are compared with available analytical models, based either on first-order perturbation theory or on a description by anomalous exponents. The simulations show better agreement to the expectations of the perturbational approach. The effect of temperature and zero-point vibrations on the acoustic out-of-plane anharmonic shifts of graphene are briefly reviewed.