ИСТИНА

A summary data on the superconducting gap parameters 2Δ_L, and 2Δ_S vs. the critical temperature Tc obtained by SNS-Andreev spectroscopy (our group) and by other groups for iron-based superconductors are presented and compared. The conclusion on gap symmetry type is made. By applying two-gap BCS-model (Moskalenko and Suhl equations) to Δ_L,S(T), the relative coupling constants are derived. It is shown by us that the intraband coupling constants are not less than interband ones. Together with the form of Andreev dI/dV-dips this fact points to the extended s-wave symmetry type without sign reversal (s++) rather than pure s- or d-wave symmetry type for gaps Δ_L and Δ_S.