Subgap states and Dynes parameter in hard-gap tunnel junctions

ORAL

Abstract

Normal metal – insulator - superconductor (NIS) tunnel junctions are the basic building blocks for Josephson junctions, superconducting qubits and many other applications. Ideally, the single particle current is zero within the superconducting gap; while photon assisted tunneling (PAT) can lead to sub-gap currents (Dynes parameter). Here, we examine hard gap NIS tunnel junctions in a well filtered and shielded environment where PAT is negligible. We observe discrete, sharp current steps in the sub-gap regime which can be used as a primary thermometer, in excellent agreement with regular NIS thermometry [1], but cooling as low as 4 mK on a nuclear refrigerator [2]. In an in-plane magnetic field, the steps exhibit Zeeman splitting with g = 2 and display diamagnetic shifts. We model the steps as geometric resonances within the weakly disordered normal metal giving enhanced Andreev reflection due to multiple reflections. The model shows that disorder is a possible microscopic origin for Dynes-type linear leakage current.
[1] A. V. Feshchenko at al., Phys. Rev. Appl. 4, 034001 (2015).
[2] M. Palma, C. P. Scheller, at al., Appl. Phys. Lett. 11, 253101 (2017).

*This work acknowledges founding from the Swiss NSF, NCCR QSIT, the Swiss Nanoscience Institute, the Europeam Microkelvin Platform

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Presenters

  • Christian Scheller

    • University of Basel
    • Department of Physics, Univ of Basel
    • University of Basel, Department of Physics

Authors

  • Christian Scheller

    • University of Basel
    • Department of Physics, Univ of Basel
    • University of Basel, Department of Physics

  • Mario Palma

    • Department of Physics, University of Wisconsin-Madison
    • University of Basel, Department of Physics

  • Lucas Casparis

    • Microsoft
    • Niels Bohr Institute, Univ of Copenhagen
    • Niels Bohr Institute
    • Center for Quantum Devices and Microsoft Quantum Lab–Copenhagen, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
    • Microsoft Quantum Research, Copenhagen

  • Taras Patlatiuk

    • University of Basel
    • Department of Physics, Univ of Basel

  • Luca Chirolli

    • IMDEA-Nanoscience

  • Anna V Feshchenko

    • Department of Applied Physics, Aalto University
    • Aalto University, Low Temperature Laboratory

  • Dario Maradan

    • Physikalisch-Technische Bundesanstalt (PTB)
    • University of Basel, Department of Physics

  • Matthias Meschke

    • Department of Applied Physics, Aalto University
    • Aalto University, Low Temperature Laboratory

  • Jukka P Pekola

    • Aalto University
    • QTF Centre of Excellence, Department of Applied Physics, Aalto University
    • QTF Centre of Excellence, Aalto University
    • Department of Applied Physics, Aalto University

  • Dominik Zumbuhl

    • University of Basel
    • Department of Physics, Univ of Basel
    • University of Basel, Department of Physics
    • Department of Physics, University of Basel
    • Physics, University of Basel