Ultrafast and Low-Threshold THz Mode Switching of Two-Dimensional Nonlinear Metamaterials

Area of Science:

• Terahertz (THz) metamaterials
• Nonlinear optics
• Semiconductor physics

Background:

• Two-dimensional THz metamaterials enhance electromagnetic fields, inducing nonlinear responses in semiconductors.
• Nonlinear transport phenomena like intervalley scattering, impact ionization, and interband tunneling are implicated.
• The dynamics and timescales of resulting mode switching in metamaterial behavior remain under investigation.

Purpose of the Study:

• To identify dominant carrier generation processes in semiconductors under THz metamaterial excitation.
• To determine the fastest time constants associated with metamaterial mode switching.
• To elucidate the mechanisms driving nonlinear responses in THz metamaterial-semiconductor systems.

Main Methods:

• Fabrication of metallic split-ring resonators with nanometer-sized gaps on intrinsic semiconductors with varying bandgaps.
• Nonlinear THz time-domain spectroscopy.
• Computational simulations.

Main Results:

• Identification of the most relevant carrier generation mechanisms responsible for nonlinear responses.
• Determination of the fastest time constant for mode switching, measured at approximately one hundred femtoseconds.
• Correlation between semiconductor bandgaps and carrier generation processes.

Conclusions:

• Dominant carrier generation mechanisms and their dynamics in THz metamaterial-semiconductor interactions have been elucidated.
• The study establishes a rapid timescale for mode switching, crucial for device applications.
• Findings pave the way for developing high-speed, optically driven modulators operating in the terahertz bandwidth.