Observation of gate-tunable coherent perfect absorption of terahertz radiation in graphene

TL;DR

This paper demonstrates electrically tunable coherent perfect absorption of terahertz radiation in graphene using a specially designed cavity, enabling high absorption and modulation for potential active THz optoelectronic devices.

Contribution

The study introduces a novel electrically-tunable THz cavity with graphene, achieving near-perfect absorption and enabling detailed Fermi energy-dependent transport measurements.

Findings

Achieved 99% absorption at 2.8 THz via ionic gating

Demonstrated large modulation in THz reflectivity with low losses

Measured Fermi energy dependence of transport scattering time

Abstract

We report experimental observation of electrically-tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1eV and to achieve critical coupling condition at 2.8 THz with absorption of 99%. With the enhanced THz absorption, we were able to measure the Fermi energy dependence of the transport scattering time of highly doped graphene. Furthermore, we demonstrate flexible active THz surfaces that yield large modulation in the THz reflectivity with low insertion losses. We anticipate that the gate-tunable CPA will lead efficient active THz optoelectronics applications.