Abstract
We investigate the electronic properties and the superconducting gap characteristics of a single crystal of hole-doped 122 Fe-pnictide Ba0.65Na0.35Fe2As2 by means of specific-heat measurements. The specific heat exhibits a pronounced anomaly around the superconducting transition temperature T-c = 29.4 K and a small residual part at low temperature. In a magnetic field of 90 kOe, the transition is broadened and T-c is lowered insignificantly by an amount similar to 1.5 K. We estimate a high electronic coefficient in the normal state with a value 57.5 mJ mol(-1) K-2, being consistent with hole-doped 122 compounds. The temperature-dependent superconducting electronic specific heat cannot be described with single-gap BCS theory under the weak-coupling approach. Instead, our analysis implies a presence of two s-wave-like gaps with magnitudes Delta(1)(0)/k(B)T(c) = 1.06 and Delta(2)(0)/k(B)T(c) = 2.08 with respective weights of 48% and 52%. While our results have qualitative similarities with other hole-doped 122 materials, the gap's magnitude and their ratio are quite different.