Role of Sn impurity on electronic topological transitions in 122 Fe-based superconductors

We show that only a few percentage of Sn doping at the Ba site on BaFe₂As₂, can cause electronic topological transition, namely, the Lifshitz transition. A hole like d_xy band of Fe undergoes electron like transition due to 4% Sn doping. Lifshitz transition is found in BaFe₂As₂ system around all the high symmetry points. Our detailed first principles simulation predicts absence of any Lifshitz transition in other 122 family compounds like SrFe₂As₂, CaFe₂As₂ in agreement with experimental observations. This work bears practical significance due to the facts that a few percentage of Sn impurity is in-built in tin-flux grown single crystals method of synthesizing 122 materials and inter-relationship among the Lifshitz transition, magnetism and superconductivity. - Highlights: • Electronic topological transition due to Sn contamination in BaFe₂As₂. • Hole like Fe-d_xy band converts into electron like in 3% Sn contaminated BaFe₂As₂. • Electron like Fe-d_xz, d_yz bands moves above Fermi Level at X,Y points. • No Lifshitz transition found in Sn-contaminated Sr-122, Ca-122 systems.