Ultrasensitive Photoresponse of Graphene Quantum Dot in the Coulomb Blockade Regime to THz Radiation

TL;DR

This paper demonstrates that graphene quantum dots exhibit an ultrasensitive photoresponse to terahertz radiation in the Coulomb blockade regime, driven by a photogating effect, with minimal thermal influence, at very low temperatures.

Contribution

It is the first to explore THz photon interaction with GQDs in the Coulomb blockade regime, revealing a highly sensitive, non-thermal photoresponse mechanism.

Findings

Photocurrent response of nanoampere range to ~10 pW THz radiation.

Chemical potential renormalization of ~0.15 meV due to THz illumination.

Absence of thermal effects indicates coherent quantum phenomena.

Abstract

Graphene quantum dots (GQDs) have recently attracted considerable attention, with appealing properties for terahertz (THz) technology. This includes the demonstration of large thermal bolometric effects in GQDs when illuminated by THz radiation. However, the interaction of THz photons with GQDs in the Coulomb blockade regime - single electron transport regime - remains unexplored. Here, we demonstrate the ultrasensitive photoresponse to THz radiation (from <0.1 to 10 THz) of a hBN-encapsulated GQD in the Coulomb blockade regime at low temperature (170 mK). We show that THz radiation of $\sim$10 pW provides a photocurrent response in the nanoampere range, resulting from a renormalization of the chemical potential of the GQD of $\sim$0.15 meV. We attribute this photoresponse to an interfacial photogating effect. Furthermore, our analysis reveals the absence of thermal effects, opening new directions in the study of coherent quantum effects at THz frequencies in GQDs.