Influence of Multi-orbitals, Coulomb Correlations and Hund’s Coupling on Transition Temperature in Doped Fe-Based Superconductors

Abstract

The present paper deals with the theoretical analysis of superconducting transition temperature (T c) within two-orbital-per-site model Hamiltonian in iron-based superconductors. The Green’s function approach within the Bardeen-Cooper-Schrieffer (BCS) mean-field approximation has been applied. The expression of superconducting transition temperature has been obtained as a function of hopping parameters, onsite Coulomb interactions, and Hund’s coupling term. It is pointed out that the transition temperature decreases with increasing nearest neighbor hopping (t 1), next nearest neighbor hopping (t 3), and also with onsite Coulomb interactions. While on increasing nearest neighbor hopping between π-orbitals (t 2), the transition temperature initially increases linearly and acquire a maximum value (at t 2 = 0.065 eV), thereafter T c shows suppression. The present transition temperature analysis can be connected with the pressure-dependent (nearest and next nearest neighbor coupling) parameters (in the band structure) in iron-based systems. Further, the transition temperature increases with increasing the hybridization energy, Hund’s coupling term, and carrier density ( ) per site. Finally, the theoretically obtained results on T c have been viewed in terms of experimental variation of T c under pressure and existing theoretical predictions in iron-based superconductors.