Anomalous metallic oxygen band in the potential superconductor KCa2Fe4As4O2: A DFT study

The electronic structure, magnetism and Fermi surface of a hole self-doped potential iron-based superconductor KCa2Fe4As4O2 (12442) were studied by a first-principles DFT/GGA approach. The self-doping value is obtained from DFT is 0.75 hole on Fe-3d states for KCa2Fe4As4O2. Surprisingly, for the KCa2Fe4As4O2 it was found that except the Fe-3d bands the O-2p bands also cross the Fermi level, which is quite anomalous behavior for O-2p states. In general, the O-2p states are usually fully occupied in transition metal oxides. Here it is not the case due to the fact that CaO layer gives some of the electrons to the FeAs layer, thus leaving O-2p states partially occupied. The O-2p states form additional Fermi surface sheet with propeller-like shape around Γ-point and modify the Fe-3d Fermi surface sheets due to the hybridization. To prove the presence of anomalous metallic O-2p band in KCa2Fe4As4O2 the comparative study with the same family systems KCa2Fe4As4F2 and RbGd2Fe4As4O2 (where it is not the case) was performed. Finally, we discuss the main differences between the emergence of the metallic O-2p band in case of KCa2Fe4As4O2 and those in case of cuprate superconductors LaBaCuO4 and YBa2Cu3O7. Therefore, we expect that the KCa2Fe4As4O2 might be a potential superconductor with unusual properties.