Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 54: Focused Session: Magnetism & Superconductivity in Fe-based Pnictides and Chalcogenides (jointly with MA)
TT 54.5: Topical Talk
Donnerstag, 14. März 2013, 11:45–12:15, H20
Charge Dynamics in 122 Iron Pnictides — •Aliaksei Charnukha, Oleg V. Dolgov, Paul Popovich, Dunlu Sun, Chengtian Lin, Alexander Yaresko, Bernhard Keimer, and Alexander V. Boris — Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany
We report the full complex dielectric function of high-purity Ba0.68K0.32Fe2As2 single crystals with Tc=38.5 K determined by broadband spectroscopic ellipsometry at temperatures 10≤ T≤300 K. We discuss the microscopic origin of superconductivity-induced infrared optical anomalies in the framework of a multiband Eliashberg theory with two distinct superconducting gap energies, 2ΔA≈6 kBTc and 2ΔB≈2.2 kBTc. The observed unusual suppression of the optical conductivity in the superconducting state at energies up to 14 kBTc can be ascribed to spin-fluctuation–assisted processes in the clean limit of the strong-coupling regime. We further observe a superconductivity-induced suppression of an absorption band at an energy of 2.5 eV, two orders of magnitude above the superconducting gap energy 2Δ≈20 meV, which challenges one of the central notions of conventional theories of superconductivity. We argue that the observed superconductivity-induced suppression involves a redistribution of electronic population between bands with different orbital character. Our results emphasize the importance of orbital physics for the mechanism of superconductivity in the iron-based superconductors.