Features of the Multigap Superconductivity in Cobalt-Doped NaFeAs

The behavior of the critical current density is studied in a self-field of a single-crystal NaFe 1 – x Co x As ( T c = 21.1 K) sample in the temperature range from 4 K to T c . Within the Bardeen–Cooper–Schrieffer (BCS) model, the dependences of the superconducting carrier density ρ s ( T ) are obtained under the assumption of the two-band case. It is shown in the case of two-gap uperconductivity, the experimental data are well described by the theory, and the superconducting gaps Δ(0) obtained by approximation are in agreement with the values determined by studying the Andreev reflection spectra.