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arXiv · 1601.00672

Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

J. Gramich·A. Baumgartner·C. Schönenberger
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Abstract

We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube (CNT) quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor's finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multi-layer contacts, which result in reproducibly large and "clean" superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD.

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J. Gramich, A. Baumgartner, C. Schönenberger. 2016-04-25. Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices. https://doi.org/10.1063/1.4948352

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