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TT: Fachverband Tiefe Temperaturen
TT 21: Focus Session: Strongly Disordered Superconductors
TT 21.3: Invited Talk
Tuesday, March 19, 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 RN ≃ 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 RN ≃ 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