Department of Mechanical Engineering, Boston University, 110 Cummington Street, Boston, Massachusetts 02215, USA.
Phys Rev Lett. 2013 May 24;110(21):217404. doi: 10.1103/PhysRevLett.110.217404. Epub 2013 May 21.
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.
我们在太赫兹频率下展示了砷化镓上的非线性超材料分裂环谐振器（SRR）。对于掺杂砷化镓薄膜上的 SRR，峰值场强约为 20-160 kV/cm 的太赫兹辐射会引发带间散射。这会降低载流子迁移率，并由于掺杂薄膜的电导率降低而增强 SRR LC 响应。在超过 160 kV/cm 时，SRR 间隙内的电场增强会导致有效的碰撞电离，增加载流子密度和电导率，从而抑制 SRR 共振。我们在半绝缘砷化镓上展示了 SRR 间隙中载流子密度增加了 10 个数量级。此外，我们表明在碰撞电离区，随着太赫兹场强的增加，有效介电常数可以从负值变为正值，从而为非线性超材料开辟了新的可能性。
