Regensburg 2025 – scientific programme
Parts | Days | Selection | Search | Updates | Downloads | Help
TT: Fachverband Tiefe Temperaturen
TT 5: Superconductivity: Properties and Electronic Structure I
TT 5.7: Talk
Monday, March 17, 2025, 11:00–11:15, H36
Superfluid stiffness in strongly disordered NbN superconducting films — •Alexander Weitel Weitzel1, Lea Pfaffinger1, Matthias Stosiek2, Animesh Panda3, Ferdinand Evers3, and Christoph Strunk1 — 1Inst. of Exp. a. Appl. Phys., University of Regensburg, D-93040 Regensburg, Germany — 2TUM Sch. of Nat. Sci., Dep. of Phys. PH-I, D-85748 Garching bei München — 3Inst. of Theoretical Phys., University of Regensburg, D-93040 Regensburg, Germany
In BCS-superconductors, the spectral gap, Eg, the pairing amplitude, Δ, and the mean-field critical temperature Tc0 are essentially identical. At strong disorder, close to the superconductor-insulator transition (SIT), this is no longer the case. Moreover, in BCS-theory the superfluid stiffness, Js, is determined by Δ and normal state resistance RN. Also this relation typically no longer holds close to SIT. Recently, we have experimentally determined Js(T) in ultra-thin NbN films by measuring kinetic inductance and found a sharp Berezinski-Kosterlitz-Thouless (BKT) transition. Our latest experimental data cover Js(T ) over a wide range of disorder strength, up to normal state resistance ∼ h/e2. We find a sharp BKT-transition right up to the SIT and independently measure the characteristic scales Eg, Js, Tc0 and TBKT over two orders of magnitude in RN. We present complementary numerical calculations of the superfluid stiffness, obtained from the Boguliubov-de Gennes (BdG) theory of disordered samples in a very broad range of disorder strengths. A detailed comparison of our measurements with the computational results will be presented.
Keywords: Superconductor-Insulator transition (SIT); Berezinskii-Kosterlitz-Thouless (BKT) transition; Niobium Nitride (NbN) thin films