Superconductivity in K- and Na-doped BaFe2As2: What can we learn from heat capacity and pressure dependence of Tc

A brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at Tc for two related families of iron-based superconductors, Ba1-xKxFe2As2 (0.2 ≤ x ≤ 1.0) and Ba1-xNaxFe2As2 (0.2 ≤ x ≤ 0.9) will be given. For Ba1-xKxFe2As2 the specific heat capacity jump at Tc measured over the whole extent of the superconducting dome shows clear deviation from the empirical, $\Delta C_p (T_c) \propto T_c^3$, scaling (known as the BNC scaling) for x > 0.7. At the same concentrations range apparent equivalence of effects of pressure and K-substitution on Tc fails. These observations suggests a significant change of the superconducting state for x > 0.7. In contrast, the data for the large portion of Ba1-xNaxFe2As2 (0.2 ≤ x ≤ 0.9) series follow the BNC scaling. However, the pressure dependence of Tc (measured up to ~12 kbar) have clear nonlinearities for Na concentration in 0.2–0.25 region, that may be consistent with Tc crossing the phase boundaries of ...