Superconducting gap structure of slightly overdoped NaFe_0.955Co_0.045 As pnictides: joint SnS-Andreev spectroscopy and specific heat study

We present a study of the superconducting order parameter in slightly overdoped alkali-metal-based pnictides NaFe0.955Co0.045As with T-c approximate to 21 K using a combination of incoherent multiple Andreev reflection effect (IMARE) spectroscopy of planar SnS-junctions and specific heat measurements. We observe a multiple-gap superconductivity, directly and locally determine the magnitudes Delta(i)(0), characteristic ratios 2 Delta(i)(0)/k(B)T(c), and temperature dependences Delta(i)(T)of the superconducting order parameters. Possible momentum dependence of the revealed gaps is discussed. We show that a usage of the characteristic ratios obtained in the IMARE experiment provides a qualitative fit of the extracted temperature dependence of the electronic specific heat C-el(T)/T within the two-band approach using only two free parameters.