Pump-induced terahertz anisotropy in bilayer graphene

TL;DR

This study explores how strong terahertz fields induce anisotropic nonlinear electron dynamics in doped bilayer graphene, revealing polarization-dependent effects and modeling them with semiclassical and Boltzmann approaches.

Contribution

It demonstrates the pump-induced anisotropy in bilayer graphene and models the effect using semiclassical and Boltzmann simulations, providing insight into electron dynamics under terahertz excitation.

Findings

Differential pump-probe signals depend on polarization alignment.

Anisotropy arises from differences in electron effective mass in k-space.

Models agree qualitatively with experimental observations.

Abstract

We investigate the intraband nonlinear dynamics in doped bilayer graphene in the presence of strong, linearly-polarized, in-plane terahertz fields. We perform degenerate pump-probe experiments with 3.4 THz fields on doped bilayer graphene at low temperature (12 K) and find that when the pump is co-polarized with the probe beam, the differential pump-probe signal is almost double that found in the cross-polarized case. We show that the origin of this pump-induced anisotropy is the difference in the average electron effective mass in the probe direction when carriers are displaced in k-space by the pump either parallel or perpendicular to the direction of the probe polarization. We model the system using both a simple semiclassical model and a Boltzmann equation simulation of the electron dynamics with phenomenological scattering and find good qualitative agreement with experimental results.