Theoretical Investigation of the Superconducting and Thermodynamic Properties of Two-Band Model High-Temperature Iron-Based Superconductor Ba_1-xNa_xFe₂As₂

This work presents the theoretical investigation of the superconducting and thermo-dynamic properties of the two-band model high-temperature iron-based superconductor Ba_1-xNa_xFe₂As₂. By developing a model Hamiltonian and by employing the well-known double-time temperature-dependent Green's function formalism, we have computed the superconducting order parameters for the electron and hole intra- and inter-band transitions, superconducting transition temperature, densities of states, and condensation energies. Furthermore, the electronic specific heat and the entropy for electron and hole intra-band transitions have been determined. By using appropriate experimental data and some credible approximations of the parameters in the computed expressions, we have found the phase diagrams of superconducting order parameters versus the temperature, superconducting critical temperature versus the inter-band interaction potential, temperature dependences of the electronic specific heat and entropy for electron and hole intra-band transitions, and densities of states for the electron and hole intra-band transitions as functions of the excitation energy at different values of the temperature. Finally, the phase diagrams of the condensation energy versus the temperature, inter-band pairing potential at T = 0 K versus the condensation energy, and condensation energy versus the superconducting transition temperature (TC)have been drawn. In some of the phase diagrams, the comparison between theoretical and experimental values has been made. The results are in a good agreement with previous findings. (author)