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

Abstract

We have measured the conductance and shot noise of superconductor-normal metal (S-N) junctions between a niobium (Nb) film and a two-dimensional electron gas (2DEG), formed in an InAs-based semiconductor heterostructure. Adjacent to the junction, the 2DEG is shaped into a sub-micrometer 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 $\ensuremath{\approx}60\text{--}70\phantom{\rule{0.2em}{0ex}}%$. The present device can be seen as a quasi-ballistic S-N beam-splitter junction.