InAs nanowire superconducting tunnel junctions: Quasiparticle spectroscopy,thermometry, and nanorefrigeration

We demonstrate an original method based on controlled oxidation for creating high-quality tunnel junctions between superconducting Al reservoirs and InAs semiconductor nanowires (NWs).We show clean tunnel characteristics with a current suppression by ＞4 orders of magnitude for a junction bias well below the Al gap of A0 ≈ 200 μeV.The experimental data agree well with the BardeenCooper-Schrieffer theoretical expectations for a superconducting tunnel junction.The studied devices employ small-scale tunnel contacts functioning as thermometers as well as larger electrodes that provide proof-of-principle active cooling of the electron distribution in the NWs.A peak refrigeration of approximately δT =10 mK is achieved at a bath temperature of Tbath ≈ 250-350 mK for our prototype devices.This method introduces important perspectives for the investigation of the thermoelectric effects in semiconductor nanostructures and for nanoscale refrigeration.