Abstract

For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it (for review see [1]). We will show that this metallic state can be eliminated by adequately filtering external radiation, and that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations [2].
By introducing homogeneous disorder, such films will exhibit strong, seemingly inhomogenous, local variations in the superconducting gap [3]. In the second part of the talk we will present recent, unpublished, results indicating the existence of an underlying order of these gap variations. Our results are made possible due to the high resolution in our tunneling spectroscopy measurements achieved by utilizing superconducting tips.

[1] Kapitulnik, A., Kivelson, S. A. & Spivak, B. Anomalous metals - failed superconductors. Rev. Mod. Phys.91, 011002 (2019).
[2] Tamir, I., Benyamini, A., Telford, E.J., Gorniaczyk, F., Doron, A., Levinson, T., Wang, D., Gay, F., Sacépé, B., Hone, J. and Watanabe, K. Sensitivity of the superconducting state in thin films. Science advances, 5(3), p.eaau3826 (2019).
[3] B. Sacépé, C. Chapelier, T. I. Baturina, V. M. Vinokur, M. R. Baklanov, and M. Sanquer. Disorder-induced inhomogeneities of the superconducting state close to the superconductor-insulator transition. Phys. Rev. Lett. 101, 157006 (2008).