Observation of Multi-Gap Superconductivity in GdO(F)FeAs by Andreev Spectroscopy

We have studied current-voltage characteristics of Andreev contacts in polycrystalline GdO$_{0.88}$F$_{0.12}$FeAs samples with bulk critical temperature $T_c$ = (52.5 $\pm$ 1) K using break-junction technique. The data obtained cannot be described within the single-gap approach and suggests the existence of a multi-gap superconductivity in this compound. The large and small superconducting gap values estimated at $T = 4.2$ K are $\Delta_L=10.5\pm 2$ meV and $\Delta_S$ = $2.3 \pm 0.4$ meV, respectively.