Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 40: Superconductivity: Ferropnictides 1

TT 40.11: Talk

Thursday, March 26, 2009, 16:45–17:00, HSZ 03

Momentum dependence of the superconducting gap in Ba_1−xK_xFe₂As₂ — •D. V. Evtushinsky¹, D. S. Inosov^1,2, V. B. Zabolotnyy¹, A. Koitzsch¹, M. Knupfer¹, B. Büchner¹, G. L. Sun², V. Hinkov², A. V. Boris², C. T. Lin², B. Keimer², A. Varykhalov³, A. A. Kordyuk^1,4, and S. V. Borisenko¹ — ¹Institute for Solid State Research, IFW Dresden, P. O. Box 270116, D-01171 Dresden, Germany — ²Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany — ³BESSY GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany — ⁴Institute of Metal Physics of National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine

The precise momentum dependence of the superconducting gap in the iron-arsenide superconductor with T_c=32 K (BKFA) was determined from angle-resolved photoemission spectroscopy (ARPES) via fitting the distribution of the quasiparticle density to a model. The model incorporates finite lifetime and experimental resolution effects, as well as accounts for peculiarities of BKFA electronic structure. We have found that the value of the superconducting gap is practically the same for the inner Γ-barrel, X-pocket, and “blade”-pocket, and equals 9 meV, while the gap on the outer Γ-barrel is estimated to be less than 4 meV, resulting in 2Δ/k_BT_c=6.8 for the large gap, and 2Δ/k_BT_c<3 for the small gap. We also observe that below T_c photoemission signal contains large non-superconducting part.