Heat capacity jump at Tc and pressure derivatives of superconducting transition temperaturein the Ba1−xNaxFe2As2 (0.1 x 0.9) series

We present the evolution of the initial (up to ∼10 kbar) hydrostatic pressure dependencies of Tc and of the ambient pressure, and the jump in the heat capacity associated with the superconducting transition as a function of Na doping in the Ba1-xNaxFe2As2 family of iron-based superconductors. For Na concentrations 0.15≤x≤0.9, the jump in specific heat at Tc, ΔCp|Tc, follows the ΔCpâ̂ T3 (the so-called BNC scaling) found for most BaFe2As2-based superconductors. This finding suggests that, unlike the related Ba1-xKxFe2As2 series, there is no significant modification of the superconducting state (e.g., change in superconducting gap symmetry) in the Ba1-xNaxFe2As2 series over the whole studied Na concentration range. Pressure dependencies are nonmonotonic for x=0.2 and 0.24. For other Na concentrations, Tc decreases under pressure in an almost linear fashion. The anomalous behavior of the x=0.2 and 0.24 samples under pressure is possibly due to the crossing of the phase boundaries of the narrow antiferromagnetic tetragonal phase, unique for the Ba1-xNaxFe2As2 series, with the application of pressure. The negative sign of the pressure derivatives of Tc across the whole superconducting dome (except for x=0.2) is a clear indication of the nonequivalence of substitution and pressure for the Ba1-xNaxFe2As2 series.