Density functional theory based first principles electronic structure study on 112 Fe based superconductors: Fermiology and Lifshitz transition

摘要

We study detailed electronic structure of newly invented 112 iron based superconductors within first principles density functional theory. Certain amount of doping of rare-earth elements like La in place of Ca and transition metals (Co, Ni etc.) in place of Fe are found to enhance superconductivity in this family of compounds. We have presented results of density functional theory based first principles calculations on band structure as well as Fermi surface of doped 112 materials, Ca_(1-x)La_xFe_(1-y)TM_yAs_2 for various x, y (transition metals = TM). We show that there is Lifshitz like electronic topological transition in doped 112 materials like other family of Fe-based materials observed earlier. We analyse, comparing with existing phase diagrams, possible inter-relationship between superconductivity and Lifshitz transition for various kinds of doping in these materials. We show that around certain percentage of La doping, can either lead to partial or full Lifshitz transition, causing modifications in the Fermi surface topology, affecting nesting condition as well as effective density of states. These situations are also found in La-TM-co-doped compounds. Our results reflect a possible correlation between Lifshitz transition, magnetism and superconductivity in these materials.