Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 51: Superconductivity: Tunneling, Josephson Junctions, SQUIDs
TT 51.5: Vortrag
Mittwoch, 9. März 2016, 16:00–16:15, H19
Sub-gap conductivity of disordered superconducting TaN and NbN thin films — •Marc Scheffler1, M. Maximilian Felger1, Moritz Scholze1, Uwe S. Pracht1, Martin Dressel1, Konstantin S. Ilin2, Michael Siegel2, and Lara Benfatto3 — 11. Physikalisches Institut, Universität Stuttgart — 2Institut für Mikro- und Nanoelektronische Systeme, KIT — 3ISC-CNR and Department of Physics, Sapienza University of Rome
Optical spectroscopy studies provide valuable insight into the characteristics of superconductors, such as the superconducting energy gap and the electrodynamical response of the superfluid condensate and the quasiparticles. Recently, the sub-gap optical conductivity of strongly disordered superconductors has gained substantial attention because of the possibility to observe collective modes that go beyond the classical, BCS-based predictions for the optical properties of superconductors.
We have performed broadband microwave spectroscopy on thin films of NbN (thickness between 3 nm and 20 nm; Tc between 5 K and 13 K) and TaN (thickness 5 nm; Tc around 9 K). The covered temperatures are down to 1.1 K and the frequency range goes up to 50 GHz (which is well below the energy gap). We analyze the real and imaginary parts of the frequency-dependent microwave conductivity and determine the contributions of quasiparticles and Cooper pairs, respectively. We compare these data to Mattis-Bardeen expectations and we discuss them in the light of the ongoing discussion of collective modes in superconductors.