Berlin 2015 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 21: Superconductivity: Poster Session
TT 21.6: Poster
Monday, March 16, 2015, 15:00–18:00, Poster B
THz Spectroscopy on Superconducting NbN Thin Films — •Lena Daschke1, Uwe S. Pracht1, Martin Dressel1, Marc Scheffler1, Konstantin S. Ilin2, and Michael Siegel2 — 11. Physikalisches Institut, Universität Stuttgart — 2Institut für Mikro- und Nanoelektronische Systeme, Karlsruher Institut für Technologie
Epitaxial thin-film niobium nitride (NbN) is a conventional BCS superconductor. In presence of strong disorder, however, electronic inhomogeneities appear, which is not fully understood yet. To obtain a better insight into the physics of such disordered materials, studies on model systems such as structurally tailored films might be useful. Furthermore, disordered NbN films are used for single-photon detection devices, whose proper performance depends on a profound understanding of the superconducting properties. The studied NbN films have a Tc ranging from 10 to 15 K and the superconducting energy gap is easily accessible with THz spectroscopy (0.4 - 5.6 meV).
We investigate thin films of NbN sputtered on a sapphire substrate. With a Mach-Zehnder interferometer we measure the amplitude and phase shift of radiation transmitted through the thin-film sample. From there we can determine the real and imaginary parts of the optical conductivity. These results give information about the energy gap, Cooper pair density, and quasiparticle dynamics, including the temperature evolution of these quantities. We found that a film with 10 nm thickness roughly follows the BCS behavior, as expected. We will present results of our measurements on several different NbN samples.