Enhanced electron-phonon coupling in graphene with periodically distorted lattice

TL;DR

This study demonstrates that optically-driven lattice vibrations in bilayer graphene can transiently enhance electron-phonon coupling, potentially influencing material properties like superconductivity.

Contribution

It provides experimental evidence of a three-fold transient enhancement of electron-phonon coupling via ultrafast optical lattice modulation in graphene.

Findings

Decreased Drude scattering rate upon driving

Increased relaxation rate of hot quasi-particles

Quantitative agreement with enhanced electron-phonon coupling

Abstract

Electron-phonon coupling directly determines the stability of cooperative order in solids, including superconductivity, charge and spin density waves. Therefore, the ability to enhance or reduce electron-phonon coupling by optical driving may open up new possibilities to steer materials' functionalities, potentially at high speeds. Here we explore the response of bilayer graphene to dynamical modulation of the lattice, achieved by driving optically-active in-plane bond stretching vibrations with femtosecond mid-infrared pulses. The driven state is studied by two different ultrafast spectroscopic techniques. Firstly, TeraHertz time-domain spectroscopy reveals that the Drude scattering rate decreases upon driving. Secondly, the relaxation rate of hot quasi-particles, as measured by time- and angle-resolved photoemission spectroscopy, increases. These two independent observations are quantitatively consistent with one another and can be explained by a transient three-fold enhancement of the electron-phonon coupling constant. The findings reported here provide useful perspective for related experiments, which reported the enhancement of superconductivity in alkali-doped fullerites when a similar phonon mode was driven.