Thermoelectric and viscous contributions to the hydrodynamic ratchet effect

TL;DR

This paper investigates thermoelectric and viscous effects on the radiation-induced direct current in asymmetric structures, revealing their frequency scaling, sign change potential, and plasmonic resonances, extending understanding of electron transport regimes.

Contribution

It introduces the thermoelectric contribution to the hydrodynamic ratchet effect and analyzes viscous effects, highlighting their impact on frequency dependence and plasmonic excitations.

Findings

Thermoelectric contribution causes a high-frequency $1/\omega^2$ scaling in the hydrodynamic regime.

Viscous effects scale as $1/\omega^4$ at high frequencies.

Asymmetry enables excitation of directional traveling plasmons.

Abstract

We study thermoelectric and viscous contributions to the ratchet effect, i.e. radiation-induced generation of the direct electric current, $J_{\rm rat},$ in asymmetric dual-grating gate structure without inversion center. Previously [E.M\"onch et al, Phys. Rev. B {\bf 105}, 045404 (2022)], it was demonstrated that frequency dependence of the $J_{\rm rat}$ is essentially different within hydrodynamic (HD) and drift-diffusion (DD) regimes of the electron transport: $ J_{\rm rat}^{\rm HD} \propto 1/\omega^6 $ and $ J_{\rm rat}^{\rm DD} \propto 1/\omega^2 $ for $\omega \to \infty.$ Here we analyze previously neglected thermoelectric contribution and find that it yields high-frequency asymptotic $1/\omega^2$ even in the HD regime and can change sign of the response. Account of the finite viscosity of the electron liquid yields contribution which scales at high frequency as $1/\omega^4.$ We also find plasmonic resonances in the $J_{\rm rat},$ and demonstrate that asymmetry of the structure allows for excitation of the so-called directional travelling plasmons.