Berlin 2024 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 21: Focus Session: Strongly Disordered Superconductors

TT 21.3: Hauptvortrag

Dienstag, 19. März 2024, 10:30–11:00, H 0104

Superfluid stiffness of a strongly disordered superconductor close to the superconductor-insulator transition — •Alexander Weitzel¹, Lea Pfaffinger¹, Ilaria Maccari², Klaus Kronfeldner¹, Thomas Huber¹, Lorenz Fuchs¹, Simon Reinhardt¹, James Mallord¹, Sven Linzen³, Evgeni Il’ichev³, Nicola Paradiso¹, and Christoph Strunk¹ — ¹Institute for Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany — ²Department of Physics, Stockholm University, Stockholm SE-10691, Sweden — ³Leibniz Institute of Photonic Technology, D-07745 Jena, Germany

In superconducting thin films, the superconductor-insulator transition (SIT) is a paradigmatic example of a quantum phase transition: With increasing disorder the critical temperature of the superconductor is suppressed towards zero until an insulating ground state that is expected at a critical level of disorder with normal state resistance R_N ≃ h/4e². Notably, in many materials the mechanism of the SIT is not entirely clear, with competing explanations based on suppression of the order parameter modulus or proliferation of phase fluctuations. Using a tank circuit compatible with dc transport measurements, we investigate ultra-thin atomic layer deposited NbN films and trace the evolution of the superfluid stiffness as a function of disorder close to the SIT. We observe a sharp Berezinskii-Kosterlitz-Thouless transition in dc transport and in superfluid stiffness that persists even up to R_N ≃ h/e². In the vicinity of the SIT, phase fluctuations suppress the superfluid stiffness, consistent with a bosonic mechanism of SIT.

Keywords: disordered superconductors; superconductor-insulator transition (SIT); NbN; BKT transition; superfluid stiffness