Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: SC: Iron-Based Superconductors - 122

TT 34.2: Talk

Thursday, March 25, 2010, 14:15–14:30, H20

Superconductivity induced anomalies in the dielectric response of Ba_0.68K_0.32Fe₂As₂ identified by spectral ellipsometry. — •Aliaksei Charnukha, Paul Popovich, Yulia Matiks, Oleg Dolgov, Alexander Yaresko, Dunlu Sun, Chengtian Lin, Bernhard Keimer, and Alexander Boris — Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, Stuttgart, 70569 Deutschland

Spectroscopic ellipsometry was used to study the dielectric function of a hole-doped Ba_0.68K_0.32Fe₂As₂, with a sharp (Δ T< 0.6 K) transition to the SC state below T_c≈ 38.5 K, in the spectral range 0.012 − 6.5 eV at temperatures 7−300 K. The optical conductivity spectra are dominated by a series of interband transitions, which all agree well with the predictions of LDA calculations. Our results provide clear evidence of SC gap formation in the far-infrared optical conductivity spectra, 2Δ_SC≈5.5−6.5 k_BT_c. We find the penetration depth to be 1600 Å in close agreement with the values determined by other techniques. The data also provide detailed information about the evolution of the optical self-energy in the normal and SC states. The frequency and temperature dependencies of the SC gap formation speak for the extended s_±−wave pairing symmetry with strong coupling to the intermediate boson mode centered at ≈25meV. Examination of the conductivity in the optical spectral range uncovered superconductivity-induced suppression of interband transitions at energies more than 200Δ_SC.