High field response of gated graphene at THz frequencies

TL;DR

This study investigates how the nonlinear terahertz transmission in gated graphene depends on Fermi energy and impurity scattering, revealing field-induced conductivity reduction that varies with sample type and Fermi level.

Contribution

It provides a detailed analysis of the Fermi energy and impurity scattering effects on nonlinear THz response in graphene, incorporating a comprehensive Drude model.

Findings

Transmission increases with field amplitude due to intraband absorption bleaching.

Both monolayer and multilayer graphene show strong field dependence not solely due to heating.

Fermi level significantly influences the nonlinear THz conductivity behavior.

Abstract

We study the Fermi energy level dependence of nonlinear terahertz (THz) transmission of gated multi-layer and single-layer graphene transferred onto sapphire and quartz substrates. The two samples represent two limits of low-field impurity scattering: short-range neutral and long-range charged impurity scattering, respectively. We observe an increase in the transmission as the field amplitude is increased due to intraband absorption bleaching starting at fields above 8 kV/cm. This effect arises from a field-induced reduction in THz conductivity that depends strongly on the Fermi energy. We account for intraband absorption using a free carrier Drude model that includes neutral and charged impurity scattering as well as optical phonon scattering. We find that although the Fermi-level dependence in the monolayer and five-layer samples is quite different, both exhibit a strong dependence on the field amplitude that cannot be explained on the basis of an increase in the lattice temperature alone. Our results provide a deeper understanding of transport in graphene devices operating at THz frequencies and in modest kV/cm field strengths where nonlinearities exist.