We study optical response of a plasmonic crystal based on multi-gated 2D structure with periodic modulation of the electron density in the device channel. In such a structure, the plasma wave velocity is periodically modulated as well. We consider the simplest model of periodically alternating stripes of the electron density and plasma wave velocity: active regions with high plasma wave velocity and passive regions with low plasma wave velocity. Terahertz radiation applied to such a structure excites plasmonic resonances both in the active and passive stripes. The width of the resonances is determined by the momentum relaxation rate. For sufficiently large relaxation rates, the resonances in the passive regions strongly overlap and only “active resonances” survive. In this regime, the plasmonic oscillations in the active regions exponentially decay into the passive regions, so that different active regions are disconnected at plasmonic frequencies but connected at zero dc frequency. We assume that dc current is applied to this plasmonic crystal and calculate radiation-induced correction to the dissipation in the channel. We demonstrate that with increasing the dc current this correction changes sign, which results in amplification of the optical signal.
We have developed a theory of the helicity-driven plasmonic dc response of the gated two-dimensional electron gas to the terahertz (THz) radiation. It was demonstrated that the phase difference between THz signals coupled to source and drain of the field effect transistor (TeraFET) induces a plasmon-assisted direct current (dc), which is dramatically enhanced in the vicinity of plasmonic resonances. We have also proposed an appropriate scheme for a phase-sensitive homodyne detector operating in this phase-asymmetry regime. As a key result, helicity and phase-sensitive conversion of circular polarized radiation into dc photovoltage induced by the plasmon- interference mechanism was observed: two plasma waves, excited at the source and the drain part of the transistor interfere inside of the channel. The helicity sensitive phase shift between these waves can be achieved by using an asymmetric antenna configuration. Suggested plasmonic detector is capable of measuring the phase difference between two arbitrary phase-shifted optical signals.
The electromagnetic wave impinging on the spatially modulated two-dimensional electron liquid (2DEL) induces a direct current (DC) when the wave amplitude modulated with the same wave vector as the 2DEL but is shifted in phase (the ratchet effect). The recent theory of this phenomenon predicted a dramatic enhancement at the plasmonic resonances and a non-trivial polarization dependence [1]. We will present the results of the numerical simulations using a hydrodynamic model exploring the helicity dependence of the DC current for silicon, InGaAs, and GaN metamaterial structures at cryogenic and room temperatures. In particular we will report on the effect of the DEL viscosity and explore the nonlinear effects at large amplitudes of the helical electromagnetic radiation impinging on the ratchet structures. We will then discuss the applications of the ratchet effect for terahertz metamaterials in order to realize ultra-sensitive terahertz (THz) radiation detectors, modulators, phase shifters, and delay lines with cross sections matching the terahertz wavelength and capable of determining the electromagnetic wave polarization and helicity. To this end, we propose and analyze the four contact ratchet devices capable of registering the two perpendicular components of the electric currents induced by the elliptically or circularly polarized radiation and analyze the load impedance effects in the structures optimized for the ratchet metamaterial THz components. The analysis is based on the hydrodynamic model suitable for the multi-gated semiconductor structures, coupled self-consistently with Poisson’s equation for the electric potential. The model accounts for the effects of pressure gradients and 2DEL viscosity. Our numerical solutions are applicable to the wide ranges of electron mobility and terahertz power.
[1] I. V. Rozhansky, V. Yu. Kachorovskii, and M. S. Shur, Helicity-Driven Ratchet Effect Enhanced by Plasmons, Phys. Rev. Lett. 114, 246601, 15 June 2015
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