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TT: Fachverband Tiefe Temperaturen

TT 12: Poster Session Superconductivity

TT 12.6: Poster

Montag, 11. März 2013, 15:00–19:00, Poster D

Quasi-optical THz spectroscopy on ultra-thin superconducting films of NbN and TaN. — •Uwe Santiago Pracht¹, Eric Heintze¹, Marc Scheffler¹, Martin Dressel¹, Konstantin Il'in², Dagmar Henrich², Qiao Guo², and Michael Siegel² — ¹1. Physikalisches Institut, University of Stuttgart, Germany — ²Institut für Mikro- und Nanoelektronische Systeme (IMS), Karlsruher Institut für Technologie (KIT), Germany

Ultra-thin films of the conventional superconductors niobium nitride (NbN) and tantalum nitride (TaN) have recently attracted attention for devices such as single-photon detectors. Quasi-optical THz spectroscopy is a particularly suited tool with direct access to superconducting properties, such as the superconducting energy gap, which are necessary for a proper understanding of device performance and for future improvements.

With our THz-spectroscopy approach we measure amplitude and phaseshift of coherent radiation (0.09-1.2 THz) passing through thin-film systems. We present the performance and possibilities of our experimental set-up, and we apply it to ultra-thin superconducting films of NbN and TaN. We fit the experimental data to weak-coupling BCS theory, and we obtain frequency- and temperature-dependent superconducting properties such as the complex optical conductivity, the complex dielectric function, the energy gap, the penetration depth, and the superfluid density.