Giant terahertz photoconductance of tunneling point contacts

TL;DR

This paper reports a significant increase in conductance of a quantum point contact in the tunneling regime when exposed to terahertz radiation, explained by photon-mediated tunneling mechanisms.

Contribution

It presents the first observation of giant terahertz-induced photoconductance in tunneling quantum point contacts and provides a theoretical explanation for the effect.

Findings

Conductance increases by two orders of magnitude under terahertz irradiation.

The effect shows superlinear intensity dependence and polarization sensitivity.

Experimental results align well with photon-mediated tunneling theory.

Abstract

We report on the observation of the giant photoconductance of a quantum point contact (QPC) in tunneling regime excited by terahertz radiation. Studied QPCs are formed in a GaAs/AlGaAs heterostructure with a high-electron-mobility two-dimensional electron gas. We demonstrate that irradiation of strongly negatively biased QPCs by laser radiation with frequency f = 0.69 THz and intensity 50 mW/cm^2 results in two orders of magnitude enhancement of the QPC conductance. The effect has a superlinear intensity dependence and increases with the dark conductivity decrease. It is also characterized by strong polarization and frequency dependencies. We demonstrate that all experimental findings can be well explained by the photon-mediated tunneling through the QPC. Corresponding calculations are in a good agreement with the experiment.