Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs

摘要

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