Electronic structure and magnetism of K-intercalated iron chalcogenides

Abstract

We theoretically investigate the electronic and magnetic structure of vacancy bearing K-intercalated Fe chalcogenides ($\text{Ch}=\text{Se}$ and Te) using first-principles calculations. Motivated by experimental report on the compositions and suggested Fe valences of the parent insulating and superconducting phases on vacancy bearing K-intercalated Fe selenides, we consider three compositions, ${\mathrm{KFe}}_{1.5}{\mathrm{Ch}}_{2}, {\mathrm{K}}_{0.94}{\mathrm{Fe}}_{1.5}{\mathrm{Ch}}_{2}$, and ${\mathrm{KFe}}_{1.56}{\mathrm{Ch}}_{2}$. The electronic structure calculated on geometry optimized crystal structure of ${\mathrm{KFe}}_{1.56}{\mathrm{Se}}_{2}$ is found to be markedly different from the other two compositions due to formation of the ferromagnetic one-dimensional chain of Fe atoms in the case of ${\mathrm{KFe}}_{1.56}{\mathrm{Se}}_{2}$ as opposed to trimer geometry of Fe atoms in ${\mathrm{KFe}}_{1.5}{\mathrm{Se}}_{2}$ and ${\mathrm{K}}_{0.94}{\mathrm{Fe}}_{1.5}{\mathrm{Se}}_{2}$. This is expected to have an important bearing on the composition specific observation of superconducting properties in vacancy bearing K-intercalated Fe selenides. Interestingly, the Te compounds, which are yet to be synthesized, show very similar magnetic properties as in Se compounds, in marked contrast to 11 compounds, FeSe and FeTe. This hints that unlike FeTe, vacancy bearing K-intercalated Fe tellurides may be potential candidates for exploring superconductivity.