Study of the Two-Gap Superconductivity in GdO(F)FeAs by ScS-Andreev   Spectroscopy
  Current-voltage characteristics and dynamic conductance of the superconductor - constriction - superconductor junctions in GdO(F)FeAs polycrystalline samples with critical temperatures Tc^local = 46 - 53 K were investigated. Two superconducting gaps, the large Delta_L = 10.5 +- 2 meV, and the small one Delta_S = 2.3 +- 0.4 meV were clearly observed at T = 4.2 K. The 2Delta_L/kTc^local = 5.5 +- 1 ratio gives support to the strong coupling mechanism which is responsible for the high Tc value. Temperature dependence of the large gap Delta_L(T) indicates the presence of intrinsic proximity effect (in k-space) between two superconducting condensates. 
T.E. Shanygina, Ya.G. Ponomarev, S.A. Kuzmichev, M.G. Mikheev, S.N.   Tchesnokov, O.E. Omel'yanovsky, A.V. Sadakov, Yu.F. El...
cond-mat.supr-con