ИСТИНА

This study includes results on LiFeAs and RbFe2Se2 superconductors, obtained by SNS-Andreev spectroscopy. A summary data on the superconducting gap parameters 2Δ_L and 2Δ_S vs. the critical temperature Tc for iron-based superconductors are presented and compared. Scaling of superconducting gaps with Tc for iron-based superconductors is obvious. The BCS-ratio of the “leader” gap 2Δ_L/kBTc = 5 ± 1 point to strong electron-boson coupling; 2ΔS/kBTc = 1.1 ± 0.4. We used local value for Tc when possible; it means the Tc namely of contact region (less than 50 nm in diameter) under study. The value of local Tc is obtained by BCS-like fits of the gap temperature dependences Δ_L,S(T).