ИСТИНА

Current-voltage characteristics (CVCs) of Andreev superconductor-constriction-superconductor (ScS) nanocontacts in polycrystalline samples of FeSe (Tc = (12 ± 1) K) [1] and LaO0.9F0.1FeAs (Tc = 27 - 29 K) [2] have been measured using a break-junction technique. Two sets of subharmonic gap structures were detected due to multiple Andreev reflections indicating the existence of two nodeless superconducting gaps in both iron-based superconductors (at T = 4.2 K in FeSe deltaL = 2.7 ± 0.3 meV, deltaS = 0.8 ± 0.2 meV; in LaO0.9F0.1FeAs: deltaL = 5.5 ± 1 meV, deltaS = 1 ± 0.2 meV). Well-shaped CVCs for stacks of Andreev contacts with the number of contacts up to five were observed due to the layered structure of investigated superconductors (intrinsic multiple Andreev reflections effect). A linear relation between the superconducting gap deltaL and the magnetic resonance energy Emagres [3] in a wide range of critical temperatures is found to be valid (Emagres ? 2deltaL). According to the theoretical analysis of Onari at al. [4] this result supports the version of fully gapped s-wave state without sign reversal for iron-based superconductors.