Band-filling and correlation controlling electronic properties and magnetism in K${}_x$Fe${}_{2-y}$Se${}_2$: A slave boson study

In this paper we investigate the electronic and magnetic properties of K${}_x$Fe${}_{2-y}$Se${}_2$ materials at different band fillings utilizing the multi-orbital Kotliar-Ruckenstein’s slave-boson mean field approach. We find that at three-quarter filling, corresponding to KFe${}_2$Se${}_2$, the ground state is a paramagnetic bad metal. Through band renormalization analysis and comparison with the angle-resolved photoemission spectra data, we identify that KFe${}_2$Se${}_2$ is also an intermediate correlated system, similar to iron-pnictide systems. At two-third filling, corresponding to the Fe${}^{2+}$-based systems, the ground state is a striped antiferromagnetic (SAFM) metal with spin density wave gap partially opened near the Fermi level. In comparison, at half filling case, corresponding to the Fe${}^{3+}$-based compounds, besides SAFM, a $N\acute{e}el$ antiferromagnetic metallic ground state without orbital ordering is observed in the intermediate correlation range, and an orbital selective Mott phase (OSMP) accompanied with an intermediate-spin to high-spin transition is also found. These results demonstrate that the band filling and correlation control the electronic state, Fermi surface topology and magnetism in K${}_x$Fe${}_{2-y}$Se${}_2$.