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, $\gamma ,$ is large compared to fundamental gate-tunable frequencies ${\omega }_{1,2}$ 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 $(\omega ,{\omega }_2)$ for fixed ${\omega }_1$ is constructed. Most importantly, $\mathcal{T}$ sharply depends on the gate voltages and frequency. In particular, for ${\omega }_2\ll {\omega }_1,$ $\mathcal{T}$ strongly varies on the very small frequency scale, $\delta \omega \ll \gamma ,$ determined by the Maxwell relaxation, $\delta \omega \sim {\omega }_1^2/\gamma ,$ so that the superlattice shows high responsivity within the frequency band $\delta \omega .$

7 pages, 2 figures