Electronic structure of prototype AFe$_2$As$_2$ and ReOFeAs high-temperature superconductors: a comparison

We have performed ab initio LDA calculations of electronic structure of newly discovered prototype high-temperature superconductors AFe$_2$As$_2$ (A=Ba,Sr) and compared it with previously calculated electronic spectra of ReOFeAs (Re=La,Ce,Pr,Nd,Sm). In all cases we obtain almost identical densities of states in rather wide energy interval (up to 1 eV) around the Fermi level. Energy dispersions are also very similar and almost two-dimensional in this energy interval, leading to the same basic (minimal) model of electronic spectra, determined mainly by Fe $d$-orbitals of FeAs layers. The other constituents, such as A ions or rare earths Re (or oxygen states) are more or less irrelevant for superconductivity. LDA Fermi surfaces for AFe$_2$As$_2$ are also very similar to that of ReOFeAs. This makes the more simple AFe$_2$As$_2$ a generic system to study high-temperature superconductivity in FeAs – layered compounds.