Topological superconductivity in LaFe2As2 and LaBaFe4As4 studied by DFT+DMFT first-principles calculations

Abstract

We investigate the electronic structure and topological properties of iron-based superconductors LaFe2As2 using density functional theory plus dynamical mean-field theory. We find that the uncollapsed tetragonal LaFe2As2 is in a nontrivial Z2 topological phase and has topological Dirac surface states near the Fermi energy which suggests there could be Majorana zero modes in the superconducting LaFe2As2. In light of the nontrivial topological properties and superconductivity of LaFe2As2 and CaKFe4As4, we predict a new iron-based compound LaBaFe4As4 and find it possesses two sets of topological Dirac surface states near the Fermi energy despite of a trivial Z2 topological index. These topological surface states are induced by a nontrivial high-order topological index Z8, a new mechanism that is distinct from all-known iron-based superconductors. Our study not only demonstrates that both LaBaFe4As4 and uncollapsed tetragonal LaFe2As2 can be good platforms for exploring topological superconductivity but also paves a new way to realize it with a nontrivial high-order topological index.

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