Ab-intio study of ultrafast charge dynamics in graphene

TL;DR

This study uses advanced simulations to analyze ultrafast charge dynamics in graphene, revealing that electron behavior is primarily governed by the π-band during intense laser pulses, and demonstrating the effectiveness of the transient electron momentum density as an experimental observable.

Contribution

It provides the first direct comparison between electron momentum density and conduction band occupancy in graphene, validating the use of time-dependent density functional theory for ultrafast charge dynamics.

Findings

Electron dynamics are dominated by the π-band even under intense laser pulses.

Transient electron momentum density accurately describes charge excitation in graphene.

Simple tight-binding models effectively capture laser-induced electron behavior.

Abstract

Monolayer graphene provides an ideal material to explore one of the fundamental light-field driven interference effects: Landau-Zener-St\"uckelberg interference. However, direct observation of the resulting interference patterns in momentum space has not proven possible, with Landau-Zener-St\"uckelberg interference observed only indirectly through optically induced residual currents. Here we show that the transient electron momentum density (EMD), an object that can easily be obtained in experiment, provides an excellent description of momentum resolved charge excitation. We employ state-of-the-art time-dependent density function theory calculations, demonstrating by direct comparison of EMD with conduction band occupancy, obtained from projecting the time propagated wavefunction onto the ground state, that the two quantities are in excellent agreement. For even the most intense laser pulses we find that the electron dynamics to be almost completely dominated by the $\pi$-band, with transitions to other bands strongly suppressed. Simple model based tight-binding approaches can thus be expected to provide an excellent description for the laser induced electron dynamics in graphene.