Correlated electronic structure of high-temperature superconductor Ba₂CuO3+δ

Cuprate superconductors have attracted extensive attention due to high critical temperatures. Conventional cuprates typically contain perfect CuO₂ planes which are considered as a key factor to superconductivity since the superconductivity takes place in them. However, in Ba₂CuO3+δ with $δ=0.2$ and O-depleted CuO₂ planes, superconductivity still arises even with a transition temperature as high as 73 K. Using combined density functional theory and dynamical mean-field theory (DFT+DMFT) calculations, we investigated the electronic correlation and electronic structure of Ba₂CuO3.25 with alternating quasi-one-dimensional (1D) CuO planes and O-depleted CuO₂ planes. We find that although different from the usual cuprates, the Cu atoms are still dominated by a 3d⁹ configuration and the system is of a new kind of correlated single-orbital physics. The quasi-1D CuO planes, composed of parallel Cu-O chains, are slightly hole-doped quasi-1D Mott insulator, while the O-depleted CuO₂ planes are more hole doped, with a 2D correlated electronic structure, and may host superconductivity.