Electronic Structure of K$_{0.8}$Fe$_2$Se$_2$ High Temperature Superconductor

Since the synthesis of the first ones in 2008, iron-based high temperature superconductors have been the subject of many studies. This great interest is partly due to their higher, upper magnetic field, smaller Fermi surface around the $\Gamma $ point, and a larger coherence length. This work is focused on A$_{x}$Fe$_{2}$Se$_{2}$ structural superconductor (FeSe, 11 hierarchy; A=K, Cs) as recently observed. ARPES data show novel, electronic structure and a hole-free Fermi surface which is different from previously observed Fermi surface images. \textit{Ab initio} density functional theory GW method was used to simulate the electronic structure of the novel superconductor A$_{x}$Fe$_{2}$Se$_{2}$. We compare this electronic structure with those of other Fe-based superconductors. Possible explanations for the hole-free Fermi surface were discussed.