Shot-noise and conductance measurements of transparent superconductor / two-dimensional electron gas junctions

TL;DR

This study investigates the conductance and shot-noise in Nb-2DEG superconductor-normal metal junctions, revealing high interface transparency and Andreev reflection effects in a quasi-ballistic S-N beam-splitter device.

Contribution

It provides the first detailed shot-noise and conductance measurements of Nb-2DEG junctions, demonstrating high interface transparency and Andreev reflection in a quasi-ballistic setup.

Findings

High-quality Nb-2DEG interface with 60-70% transparency

Enhanced shot-noise due to Andreev reflection

Device functions as a quasi-ballistic S-N beam-splitter

Abstract

We have measured the conductance and shot-noise of superconductor-normal metal (S-N) junctions between a Niobium (Nb) film and a 2-dimensional electron gas (2DEG), formed in an InAs-based semiconductor heterostructure. Adjacent to the junction, the 2DEG is shaped into a submicrometer beam-splitter. The current shot-noise measured through one arm of the beam-splitter is found to be enhanced due to Andreev reflection. Both noise and conductance measurements indicate that the Nb-2DEG interface is of high quality with a transparency approaching approx. 60-70 %. The present device can be seen as a quasi-ballistic S-N beam-splitter junction.