Correlated electronic structure of the high-temperature superconductor Ba 2 CuO 3 + δ

Cuprate superconductors have attracted extensive attention due to high critical temperatures. Conventional cuprates typically contain perfect ${\mathrm{CuO}}₂$ planes, which are considered as a key factor to superconductivity since the superconductivity takes place in them. However, in ${\mathrm{Ba}}₂{\mathrm{CuO}}_{3+\ensuremath{\delta}}$ with $\ensuremath{\delta}=0.2$ and O-depleted ${\mathrm{CuO}}₂$ planes, superconductivity still arises even with a transition temperature as high as 73 K. Using combined density functional theory and dynamical mean-field theory calculations, we investigated the electronic correlation and electronic structure of ${\mathrm{Ba}}₂{\mathrm{CuO}}_3.25$ with alternating quasi-one-dimensional (quasi-1D) CuO planes and O-depleted ${\mathrm{CuO}}₂$ planes. We find that although different from the usual cuprates, the Cu atoms are still dominated by a $3{d}⁹$ 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 insulators, while the O-depleted ${\mathrm{CuO}}₂$ planes are more hole doped, with a two-dimensional correlated electronic structure, and may host superconductivity.