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

We investigate the electronic structure and topological properties of iron-based superconductors ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$ using density functional theory plus dynamical mean-field theory. We find that the uncollapsed tetragonal ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$ is in a nontrivial ${Z}_{2}$ topological phase and has topological Dirac surface states near the Fermi energy which suggests there could be Majorana zero modes in the superconducting ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$. In light of the nontrivial topological properties and superconductivity of ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$ and ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, we predict a new iron-based compound ${\mathrm{LaBaFe}}_{4}{\mathrm{As}}_{4}$ and find it possesses two sets of topological Dirac surface states near the Fermi energy despite of a trivial ${Z}_{2}$ topological index. These topological surface states are induced by a nontrivial high-order topological index ${Z}_{8}$, a new mechanism that is distinct from all-known iron-based superconductors. Our study not only demonstrates that both ${\mathrm{LaBaFe}}_{4}{\mathrm{As}}_{4}$ and uncollapsed tetragonal ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$ can be good platforms for exploring topological superconductivity but also paves a new way to realize it with a nontrivial high-order topological index.