Determination of superconducting gap of SmFeAsFxO1-x superconductors by Andreev reflection spectroscopy

The Superconducting gap in FeAs-based superconductor SrnFeAs(O1-xFx) (x = 0.15 and 0.30) and the temperature dependence of the sample with x = 0.15 have been measured by Andreev reflection spectroscopy. The intrinsic superconducting gap is independent of contacts while many other gap-like features vary appreciably for different contacts. The determined gap value of 2 Delta = 13.34 +/- 0.47 meV for SmFeAs(O0.85F0.15) gives 2 Delta/k(B)T(C) = 3.68, close to the BCS prediction of 3.53. The superconducting gap decreases with temperature and vanishes at T-C, in a manner similar to the BCS behavior but dramatically different from that of the nodal pseudogap behavior in cuprate superconductors. (C) 2009 Elsevier B.V. All rights reserved.