Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: SC: Iron-Based Superconductors - 122

TT 34.4: Talk

Thursday, March 25, 2010, 14:45–15:00, H20

Direct observation of superconducting energy gap in the conductivity spectra of iron-pnictide films — •Dan Wu¹, Boris Gorshunov^1,2, Philipp Kallina¹, Martin Dressel¹, A- Voronkov², Kazumasa Iida³, Silvia Haindl³, Fritz Kurth³, Ludwig Schultz³, and Bernhard Holzapfel³ — ¹1. Physikalisches Institut, Universiät Stuttgart, Germany — ²Prokhorov Institute of General Physics, Russian Academy of Sciences, Russia — ³IFW Dresden, Germany

The optical reflection, transmission and phase shift of a Ba(Fe_0.9Co_0.1)₂As₂ thin film with a superconducting transition temperature T_c=20 K was measured over a wide frequency range. The evaluated optical conductivity and permittivity show a clear evidence of the complete opening of superconducting gap 2Δ/(2πℏ c)=30 cm⁻¹. The behavior agrees very well with the BCS prediction for an s-wave superconductor with no nodes in the order parameter or additional state in the gap. The normal state conductivity shows a incoherent-like background up to mid-infrared range, which is very similar to the spectra obtained from single crystals, confirming the intrinsic property of this broad contribution in 122 pnictide systems.