Topological states and competing magnetic fluctuations in iron germanides

Abstract

The correlated multiorbital multiband electronic structures of iron-based superconductors harbor an abundance of exotic electronic states, such as spin density waves, superconductivity, topological surface states, and Majorana zero modes. In this paper, we carry out density functional theory combined with dynamical mean-field theory calculations of the electronic structures, spin dynamics, and topological properties in $\mathrm{Y}{\mathrm{Fe}}_{2}{\mathrm{Ge}}_{2}$ and MgFeGe and compare them with $\mathrm{Ba}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ and LiFeAs. We find a coexistence of ferromagnetic and antiferromagnetic spin fluctuations in $\mathrm{Y}{\mathrm{Fe}}_{2}{\mathrm{Ge}}_{2}$ and MgFeGe, which are attributed to the weakly dispersive bands just below the Fermi level. Moreover, we demonstrate that MgFeGe is in a strong topological phase and has two sets of Dirac-cone-like topological surface states on the (001) surface. The coexistence of superconductivity and nontrivial band topology in these two compounds demonstrates that it is interesting to explore topological superconductivity and Majorana zero modes in iron germanides.