Multigap Superconductivity in GdFeAsO${}_{0.88}$ Evidenced by SnS-Andreev Spectroscopy

Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy we studied superconducting properties of nearly optimal oxygen-deficient GdFeAsO${}_{0.88}$ polycrystalline samples (bulk critical temperatures $T_C^{bulk}=49÷52$,K). Temperature dependences for two superconducting gaps ${\mathrm{\Delta }}_{L,S}(T)$ ($T_C^{local}=48÷50$,K) have been measured in the range from 4.2 to 50,K. The ${\mathrm{\Delta }}_{L,S}(T)$ 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.