Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 17: Superconductivity: Properties and Electronic Structure
TT 17.1: Vortrag
Montag, 16. März 2015, 15:00–15:15, H 2053
Broadband microwave response of superconducting NbN and TaN thin films — M. Maximilian Felger1, Uwe S. Pracht1, Martin Dressel1, Konstantin Ilin2, Michael Siegel2, and •Marc Scheffler1 — 11. Physikalisches Institut, Universität Stuttgart, D-70669 Stuttgart, Germany — 2Institut für Mikro- und Nanoelektronische Systeme, Karlsruher Institut für Technologie, D-76187 Karlsruhe, Germany
Ultrathin NbN and TaN films with their peculiar superconducting behavior are of interest both for fundamental physics (e.g. concerning the superconductor-insulator transition) and novel applications (e.g. for single-photon detectors). Here microwave spectroscopy is a powerful tool to characterize essential superconducting properties and to investigate the charge dynamics (Cooper pairs and quasiparticles).
We have prepared by sputtering thin films of NbN (thickness between 3 nm and 20 nm; Tc between 5 K and 13 K) and TaN (thickness 5 nm; Tc between 8.5 K and 9.5 K) on sapphire substrates. We performed broadband microwave spectroscopy on these samples using a Corbino spectrometer at temperatures down to 1.1 K and at frequencies up to 50 GHz. From these data we determine the superconducting penetration depth and we evaluate the frequency-dependent conductivity. While many of the observed features can be described within expectations of conventional BCS theory, we also find deviations that are caused by fluctuations near the superconducting transition.