Electronic structure of one-dimensional cuprate, Sr₂CuO₃

We investigate the electronic structure of the antiferromagnetic insulator Sr₂CuO₃ combining photoemission measurements and various calculations. The results suggest that the charge transfer energy, Δ, is unusually small, placing the bare upper Hubbard band within the oxygen p bandwidth, thereby implying that this compound is the first example of a correlated covalent insulator with a finite local moment.