Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs

TL;DR

This paper demonstrates nonlinear terahertz metamaterials using GaAs split ring resonators, showing field-driven carrier dynamics that enable tunable permittivity and resonance suppression at high terahertz fields.

Contribution

It introduces a novel nonlinear metamaterial platform based on GaAs SRRs that exploits field-enhanced carrier dynamics for tunable terahertz responses.

Findings

Carrier density increases by up to 10 orders of magnitude in SRR gaps.

Resonance can be suppressed or enhanced by adjusting terahertz field strength.

Effective permittivity can be switched from negative to positive.

Abstract

We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at terahertz frequencies. For SRRs on doped GaAs films, incident terahertz radiation with peak fields of ~20 - 160 kV/cm drives intervalley scattering. This reduces the carrier mobility and enhances the SRR LC response due to a conductivity decrease in the doped thin film. Above ~160 kV/cm, electric field enhancement within the SRR gaps leads to efficient impact ionization, increasing the carrier density and the conductivity which, in turn, suppresses the SRR resonance. We demonstrate an increase of up to 10 orders of magnitude in the carrier density in the SRR gaps on semi-insulating GaAs substrate. Furthermore, we show that the effective permittivity can be swept from negative to positive values with increasing terahertz field strength in the impact ionization regime, enabling new possibilities for nonlinear metamaterials.