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TT: Fachverband Tiefe Temperaturen

TT 17: Superconductivity: Fe-based Superconductors - 122 Part 2 & Theory

TT 17.1: Vortrag

Dienstag, 27. März 2012, 09:30–09:45, H 2053

Intra-gap absorption in iron-pnictide Ba(Fe_1−xCo_x)₂As₂ films — •Sina Zapf¹, Boris Gorshunov^1,2,3, Dan Wu¹, Elena Zhukova^1,2,3, Vadim Nozdrin², Silvia Haindl⁴, and Kazumasa Iida⁴ — ¹1. Physikalisches Institut, Universität Stuttgart, Germany — ²Institute of General Physics, RAS, Russia — ³Moscow Institute of Physics and Technology, Russia — ⁴Institut für Metallische Werkstoffe, IFW Dresden, Germany

Optical measurements on Ba(Fe_1−xCo_x)₂As₂ thin films [1] indicated strong intra-gap absorption (dynamical conductivity) in the superconducting (SC) state. There, conductivity at lowest frequencies was extracted with rather large uncertainty caused by huge negative dielectric constants, which is a common problem in optical measurements of superconductors. Our aim now was to perform further, more detailed investigation on the THz response of Ba(Fe_1−xCo_x)₂As₂ films. We measured their complex transmissivity with a coherent-source Terahertz (THz) spectrometer over a wide frequency range and demonstrate a remarkable improvement in resolving the frequency and temperature dependence of the intra-gap optical conductivity. Additionally, in order to enhance the interaction of the radiation with the SC films, we have performed further measurements: Two identical films on dielectric LSAT substrates were positioned face-to-face separated by a spacer, leading to multiple Fabry-Pérot resonances. We present an analysis of such a five layer system that describes the increase in sensitivity to the dynamical conductivity and discuss the experimental challenges and improvements.
B. Gorshunov et al., Phys. Rev. B 81, 060509 (2010)