Electronic structure of new oxygen-free 38 K superconductor Ba${}_{1-x}$K${}_x$Fe$_2$As${}_2$ in comparison with BaFe$_2$As$_2$ from first principles

Based on first-principles FLAPW-GGA calculations, we have investigated the electronic structure of the newly discovered oxygen-free 38 K superconductor Ba${}_{1-x}$K$_x$Fe${}_2$As${}_2$ in comparison with a parent phase – the tetragonal ternary iron arsenide BaFe${}_2$As${}_2$. The density of states, magnetic properties, near-Fermi bands compositions, together with Sommerfeld coefficients $\gamma$ and molar Pauli paramagnetic susceptibility $\chi$ have been evaluated. The results obtained allow us to classify these systems as quasi-two-dimensional ionic metals, where conduction is strongly anisotropic, happening only in the (Fe-As) layers. According to our calculations, in the case of hole doping of BaFe${}_2$As${}_2$, the density of states at the Fermi level grows, which, possibly, may be a factor promoting the occurrence of superconductivity for Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$. On the other hand, Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ lies at the border of magnetic instability and pairing interactions might involve magnetic or orbital fluctuations.