Band filling and correlation controlling electronic properties and magnetism in KxFe2−ySe2: a slave boson study

We investigate the electronic and magnetic properties of KxFe2−ySe2 materials at different band fillings utilizing the multi-orbital Kotliar–Ruckenstein slave boson mean-field approach. We find that the ground state of KFe2Se2 is a paramagnetic (PM) bad metal with intermediate correlation, in contrast with the previous antiferromagnetic (AFM) results obtained by the local density approximation. Our PM metallic ground state suggests that KFe2Se2 is the parent phase of superconducting KxFe2−ySe2, supporting a recent scanning tunneling spectroscopy experiment. For pure Fe2+-based systems, the ground state is a striped AFM (SAFM) metal with a spin density wave gap partially opened near the Fermi level. In comparison, for Fe3+-based compounds, besides SAFM, a Néel AFM metal without orbital ordering is observed, and an orbital selective Mott phase (OSMP) accompanied by an intermediate-spin to high-spin transition is also found, giving a possible scenario of an OSMP in KxFe2−ySe2. These results demonstrate that the band filling and correlation control the Fermi surface topology, electronic state and magnetism in KxFe2−ySe2. (paper)