Electronic structure and Mott localization of iron-deficient TlFe1.5Se2 with superstructures

Electronic structure and magnetic properties for iron-deficient TlFe2-xSe2 compounds are studied by first-principles calculations. We find that for the case of x = 0.5 with a Fe vacancy ordered orthorhombic superstructure, the ground state exhibits a stripelike antiferromagnetic ordering and opens a sizable band gap if the short-ranged Coulomb interaction of Fe-3d electrons is moderately strong, manifesting a possible Mott insulating state. While increasing Fe vacancies from the x = 0 side, where the band structure is similar to that of a heavily electron-doped FeSe system, the Mott localization can be driven by kinetic energy reduction, as evidenced by the band narrowing effect. Implications of this scenario in the recent experiments on TlFe2-xSe2 are discussed.