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Suppressed Superconductivity in Ultrathin Mo2N Films due to Pair-Breaking at the Interface

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Abstract

A strong disorder characterized by a small product of the Fermi vector kF and the electron mean free l drives superconductors towards insulating state. Such disorder can be introduced by making the films very thin. Here, we present 3-nm Mo2N film with kF*l ~ 2 with a resistive superconducting transition temperature Tc = 2 K heavily suppressed in comparison with the bulk Tc. Superconducting density of states (DOS) with smeared gap-like peaks and in-gap states, so called Dynes DOS, is observed by the low-temperature tunneling spectroscopy despite a sharp resistive transition. By scanning tunneling microscope, the spectral maps are obtained and related to the surface topography. The maps show a spatial variation of the superconducting energy gap on the order of 20% which is not accidental but well correlates with the surface corrugation: protrusions reveal larger gap, smaller spectral smearing, and smaller in-gap states. In agreement with our previous measurements on ultrathin MoC films, we suggest that the film-substrate interface introducing the local pair-breaking is responsible for the observed effects and generally for the suppression of the superconductivity in these ultrathin films.

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Acknowledgements

We gratefully acknowledge helpful conversations with M. Grajcar and R. Hlubina.

Funding

This work was supported by the projects APVV-18–0358, VEGA 2/0058/20, VEGA 1/0743/19 the European Microkelvin Platform, the COST action CA16218 (Nanocohybri), and by US Steel Košice.

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Authors and Affiliations

  1. Centre of Low Temperature Physics, Institute of Experimental Physics, Slovak Academy of Sciences, SK, 04001, Košice, Slovakia

    M. Kuzmiak, M. Kopčík, F. Košuth, P. Szabó & P. Samuely

  2. Department of Physics, Faculty of Electrical Engineering and Informatics, Technical University of Košice, SK, 04001, Košice, Slovakia

    M. Kuzmiak & M. Kopčík

  3. Centre of Low Temperature Physics, Faculty of Science, P. J. Šafárik University, SK, 04001, Košice, Slovakia

    F. Košuth, V. Latyshev, V. Komanický & P. Samuely

  4. Department of Applied Physics, Aalto University, 00076, Aalto, FI, Finland

    V. Vaňo

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  1. M. Kuzmiak
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  2. M. Kopčík
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  3. F. Košuth
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  4. V. Vaňo
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  5. P. Szabó
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  7. V. Komanický
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  8. P. Samuely
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Correspondence to P. Samuely.

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Kuzmiak, M., Kopčík, M., Košuth, F. et al. Suppressed Superconductivity in Ultrathin Mo2N Films due to Pair-Breaking at the Interface. J Supercond Nov Magn 35, 1775–1780 (2022). https://doi.org/10.1007/s10948-022-06197-6

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  • DOI: https://doi.org/10.1007/s10948-022-06197-6

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