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

摘要

A brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at T-c 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 T-c measured over the whole extent of the superconducting dome shows clear deviation from the empirical, Delta C-p(T-c) proportional to 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 T-c 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 T-c (measured up to similar to 12 kbar) have clear nonlinearities for Na concentration in 0.2-0.25 region, that may be consistent with T-c crossing the phase boundaries of the emergent, narrow, antiferromagnetic/tetragonal phase. Results will be discussed in context other studies of these two related families of iron-based superconductors.