Multigap Superconductivity in GdFeAsO0.88 Evidenced by SnS-Andreev Spectroscopy

Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy we studied superconducting properties of nearly optimal oxygen-deficient GdFeAsO0.88 polycrystalline samples (bulk critical temperatures \(T_{C}^{\mathrm{bulk}} = 49\mbox{--}52~\mathrm{K}\)). Temperature dependences for two superconducting gaps Δ L,S (T) (\(T_{C}^{\mathrm{local}} = 48\mbox{--}50~\mathrm{K}\)) have been measured in the range from 4.2 to 50 K. The Δ L,S (T) dependences were found to deviate from the BCS-like function; this suggests an importance of the k-space (internal) proximity effect between the two condensates.