InAs nanowire superconducting tunnel junctions: Quasiparticle spectroscopy, thermometry, and nanorefrigeration
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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 Δ 0 ≈ 200 μeV. The experimental data agree well with the Bardeen–Cooper–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 T bath ≈ 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.
KeywordsInAs nanowire superconducting tunnel junction thermometry nanorefrigeration
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S. R., V. Z., L. S., D. E., and M. R. acknowledge the financial support by CNR, through the bilateral projects with RFBR (Russia), and by Scuola Normale Superiore. The work of E. S. is funded by the Marie Curie Individual Fellowship MSCAIFEF-ST No. 660532-SuperMag. F. G, N. L., and A. F. acknowledge the financial support of the European Research Council under the European Union’s Seventh Framework Program (No. FP7/2007-2013)/ERC Grant agreement (No. 615187-COMANCHE) and MIURFIRB2013–Project Coca (No. RBFR1379UX). I. M. acknowledges funding by the Academy of Finland grant No. 298667.
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