Microscopic theory of ultrafast dynamics of carriers photoexcited by THz and near-infrared linearly-polarized laser pulses in graphene

TL;DR

This paper develops a microscopic kinetic model to analyze ultrafast carrier and phonon dynamics in graphene under linearly polarized laser pulses, revealing the roles of drift, Coulomb scattering, and interband coherence in different excitation regimes.

Contribution

It introduces a detailed kinetic theory including drift, Coulomb scattering, and interband coherence effects, providing new insights into carrier distributions and Auger processes in graphene under ultrafast excitation.

Findings

High photon energy leads to negligible drift effects and isotropic hot-electron distributions.

Low photon energy induces significant drift and a drifted Fermi distribution within hundreds of femtoseconds.

Dynamic screening forbids certain Auger processes but allows interband coherence contributions.

Abstract

We investigate the dynamics of photoexcited carriers and nonequilibrium phonons in graphene by solving the microscopic kinetic Bloch equations. The pump and drift effects from the laser field as well as the relevant scatterings (including the Coulomb scattering with dynamic screening) are explicitly included. When the pump-photon energy is high enough, the influence of the drift term is shown to be negligible and the isotropic hot-electron Fermi distribution is established under the scattering during the linearly polarized laser pulse investigated here. However, in the case with low pump-phonon energy, the drift term is important and leads to a net momentum transfer from the electric field to electrons. Due to this net momentum and the dominant Coulomb scattering, a drifted Fermi distribution different from the one established under static electric field is found to be established in several hundred femtoseconds. We also show that the Auger process investigated in the literature involving only the diagonal terms of density matrices is forbidden by the dynamic screening. However, we propose an Auger process involving the interband coherence and show that it contributes to the dynamics of carriers when the pump-photon energy is low. In addition, the anisotropically momentum-resolved hot-phonon temperatures due to the linearly polarized light are also investigated, with the underlying physics revealed.