# Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

Gramich, J. and Baumgartner, A. and Schonenberger, C.. (2016) Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices. Applied Physics Letters, 108 (17). p. 172604.

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Official URL: http://edoc.unibas.ch/52350/

We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductors 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. Published by AIP Publishing.