Highly Superlinear Giant Terahertz Photoconductance in GaAs Quantum Point Contacts in the Deep Tunneling Regime

TL;DR

This paper reports a superlinear increase in terahertz-induced photoconductance in GaAs quantum point contacts operating in deep tunneling, with the effect attributed to barrier modulation by radiation and suppressed by magnetic resonance.

Contribution

It introduces a new observation of superlinear photoconductance in GaAs quantum point contacts and models its dependence on radiation and magnetic field effects.

Findings

Photoconductance scales exponentially with radiation intensity.

Superlinear effect occurs at very low dark conductance levels.

Magnetic field via cyclotron resonance suppresses the photoconductance.

Abstract

A highly superlinear in radiation intensity photoconductance induced by terahertz laser radiation with moderate intensities has been observed in quantum point contacts made of GaAs quantum wells operating in the deep tunneling regime. For very low values of the normalized dark conductance $G_{\rm dark}/ G_0 \approx 10^{-6}$, with the conductance quantum $G_0=2e^2/h$, the photoconductance scales exponentially with the radiation intensity, so that already at $ 100 \text{ mW}/\text{cm}^2$ it increases by almost four orders of magnitude. This effect is observed for a radiation electric field oriented along the source drain direction. We provide model considerations of the effect and attribute it to the variation of the tunneling barrier height by the radiation field made possible by local diffraction effects. We also demonstrate that cyclotron resonance due to an external magnetic field manifests itself in the photoconductance completely suppressing the photoresponse.