ИСТИНА

We report the first observation and study of intrinsic multiple Andreev reflections effect (IMARE; similar to intrinsic Josephson effect) in natural ballistic S-n-S-…-S-arrays (S = superconductor, n = normal metal) formed by “break-junction” technique in GdO(F)FeAs (T_c_bulk = 48 ÷ 53 K). Using the IMARE spectroscopy, we determined the gap values Δ_L = 11.0 ± 1.1 meV and Δ_S = 2.6 ± 0.4 meV; the new results agree well with our previous data by single SnS-contacts Andreev spectroscopy. The coincidence between the SGS minima positions for Δ_L and Δ_S provides reliability and self-consistency of our results. The BCS-ratio obtained 2Δ_L/kT_C_local = 5.0 ÷ 5.9 > 3.52 (T_C_local is the contact area critical temperature) evidences for strong electron-boson coupling in the Δ_L-bands. The slightly asymmetric SGS minima for the large gap unambiguously point to an extended s-wave symmetry for the Δ_L order parameter in GdO(F)FeAs.