Terahertz ratchet effects in graphene with a lateral superlattice

TL;DR

This paper investigates terahertz-induced ratchet effects in graphene with a lateral superlattice, demonstrating controllable photocurrents influenced by gate voltage, superlattice asymmetry, and light polarization, supported by experimental and theoretical analysis.

Contribution

It introduces a comprehensive study of terahertz ratchet effects in graphene with novel superlattice structures, combining experimental data with theoretical modeling to elucidate photocurrent mechanisms.

Findings

Ratchet photocurrent can be tuned by back gate voltage and superlattice asymmetry.

Photocurrent includes thermoratchet, linear, and circular effects sensitive to polarization.

The generation mechanism involves in-plane potential and near-field light modulation.

Abstract

Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A lateral superlatice deposited on top of monolayer graphene is formed either by periodically repeated metal stripes having different widths and spacings or by inter-digitated comb-like dual-grating-gate (DGG) structures. We show that the ratchet photocurrent excited by terahertz radiation and sensitive to the radiation polarization state can be efficiently controlled by the back gate driving the system through the Dirac point as well as by the lateral asymmetry varied by applying unequal voltages to the DGG subgratings. The ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of "linear" and "circular" ratchets, sensitive to the corresponding polarization of the driving electromagnetic force. The experimental data are analyzed for the electronic and plasmonic ratchets taking into account the calculated potential profile and the near field acting on carriers in graphene. We show that the photocurrent generation is based on a combined action of a spatially periodic in-plane potential and the spatially modulated light due to the near field effects of the light diffraction.