Lateral plasmonic superlattice in strongly dissipative regime

Abstract

We calculate transmission coefficient, $\mathcal T,$ of terahertz radiation through lateral plasmonic superlattice with a unit cell consisting of two regions with different plasma wave velocities, $s_1$ and $s_2$ ($s_1 > s_2$). We generalize theory developed earlier for resonant case to the non-resonant regime, when the scattering rate, $γ,$ is large compared to fundamental gate-tunable frequencies $ω_{1,2}$ of plasma oscillations in both regions. We find that absorption, and consequently $\mathcal T$, strongly depends on density modulation amplitude and on the frequency of the incoming radiation. We describe evolution of the absorption with increasing of radiation frequency from the quasi-static regime of very low frequency to the high-frequency regime, identify several dissipation regimes and find analytical expression for absorption, and, accordingly, for $\mathcal T,$ in these regimes. A general phase diagram of non-resonant regime in the plane $(ω,ω_2)$ for fixed $ω_1$ is constructed. Most importantly, $\mathcal T$ sharply depends on the gate voltages and frequency. In particular, for $ω_2 \ll ω_1,$ $\mathcal T$ strongly varies on the very small frequency scale, $δω\ll γ,$ determined by the Maxwell relaxation, $δω\sim ω_1^2/γ,$ so that the superlattice shows high responsivity within the frequency band $δω.$