title: Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs.
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. Furthermore, we show that the effective permittivity can be swept from negative to positive values with an increasing terahertz field strength in the impact ionization regime, enabling new possibilities for nonlinear metamaterials.
authors.affiliation: Department of Mechanical Engineering, Boston University, 110 Cummington Street, Boston, Massachusetts 02215, USA.
authors.forename: Kebin
authors.initials: K
authors.lastname: Fan
authors.forename: Harold Y
authors.initials: HY
authors.lastname: Hwang
authors.forename: Mengkun
authors.initials: M
authors.lastname: Liu
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Strikwerda
authors.forename: Aaron
authors.initials: A
authors.lastname: Sternbach
authors.forename: Jingdi
authors.initials: J
authors.lastname: Zhang
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Zhao
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Keith A
authors.initials: KA
authors.lastname: Nelson
authors.forename: Richard D
authors.initials: RD
authors.lastname: Averitt