Role of Fe–As banding in electronic structure of Co doped LiFeAs

Abstract Experiment shows that the maximum Co concentration of LiFeAs in the superconducting state is around 17%. First principles calculations show that the Fe–As bond length, c -axis length, and electronic structure change gently from 0% to 18% Co doping concentration, but suddenly undergo drastic changes at 20% Co doping. Unlike many 1111 and 122 type iron-based superconductors, the contribution of Fe 3 p orbitals to N ( E F ) has significantly surpassed that of As 4 p orbitals. The rapid decrease in N ( E F ) is associated with a sharp contraction of Fe–As bond, and Fe–As bond length has ability to independently adjust N ( E F ). The sudden contraction of Fe–As bonds leads to a reverse Lifshitz transition in band, resulting in the fracture and severe shrinkage in the inner layer of the hole Fermi surface. The originally nested structure of the hole Fermi surfaces is destroyed, which may be the main reason for the termination of superconductivity.