Quasi-particle dispersion and density of states in superconducting state of iron pnictide system

The present work deals with a theoretical analysis of quasi-particle energy spectrum and density of electronic states in iron pnictide superconductors. The tight binding model Hamiltonian containing various orbital hopping energies, onsite electronic Coulomb correlations and Hund's coupling in Fe 3d orbitals has been used. The expressions of quasi-particle energies and density of states are obtained within mean-field approximation of Green's function equation of motion approach. On the basis of numerical computation, we observed a band splitting into two well separated peaks above and below the Fermi energy in the electronic spectra. On increasing the nearest neighbor hopping, the density of states in superconducting state show enhancement of gap due to sharpening of quasi-particle peak well below and above the Fermi level. While on increasing next neighbor hopping, both the spectral peaks above and below the Fermi level show sharp increase in the spectral weight. On increasing the anisotropy in Coulomb correlations, the quasi-particle energy peak in the spectra show prominent features and support in estabilizing the superconducting state in the presence of anisotropic Coulomb correlations in iron pnictides. Finally, the theoretically obtained quasi-particle energy spectrum and density of states in iron pnictides has been viewed in terms of recent photoemission ARPES and STM data.