Ultrafast Electron-Phonon Decoupling in Graphite

TL;DR

This study reveals that ultrafast photoexcitation causes a temporary decoupling of electron-phonon interactions in graphite, leading to phonon stiffening, which is explained by first-principles calculations and observed through time-resolved spectroscopy.

Contribution

It demonstrates the ultrafast electron-phonon decoupling mechanism in graphite and links it to non-equilibrium electron-hole plasma dynamics using combined experimental and theoretical approaches.

Findings

Phonon frequency upshifts immediately after photoexcitation.

Decoupling of electron-phonon interaction causes phonon stiffening.

Relaxation to stationary phonon frequency occurs within a few picoseconds.

Abstract

We report the ultrafast dynamics of the 47.4 THz coherent phonons of graphite interacting with a photoinduced non-equilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the non-adiabatic electron-phonon interaction by creating the non-equilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast non-equilibrium electron dynamics.