Current-voltage characteristics of semiconductor-coupled superconducting weak links with large electrode separations

TL;DR

This study investigates the unique current-voltage behavior of semiconductor-coupled superconducting weak links with large electrode separations, revealing thermally activated resistance falloff and a novel proportionality to device width, suggesting fluctuation effects.

Contribution

It presents experimental observations of unconventional thermal activation in large-separation superconducting weak links and proposes a new fluctuation-based explanation involving giant shot noise.

Findings

Resistance falloff is thermally activated and slower than conventional weak links.

Activation energies are proportional to device width, contrary to existing theories.

Giant shot noise from multiple Andreev reflections may cause observed fluctuations.

Abstract

We have studied the current-voltage characteristics of superconducting weak links in which the coupling medium is the 2-D electron gas in InAs-based semiconductor quantum wells, with relatively large (typically 0.5 micron) separations between niobium electrodes. The devices exhibit Josephson-like current-voltage characteristics; however, the falloff of the differential resistance with decreasing temperature is thermally activated, and is orders of magnitude slower than for more conventional weak links. Most unexpectedly, the thermal activation energies are found to be proportional to the width of the device, taken perpendicular to the current flow. This behavior falls outside the range of established theories; we propose that it is a fluctuation effect caused by giant shot noise associated with multiple Andreev reflections. The possibility of non-equilibrium effects is discussed.