t-J model on the effective brick-wall lattice for the recently discovered high-temperature superconductor Ba2CuO3+delta

Layered copper oxides have the highest superconducting transition temperatures at ambient pressure. Its mechanism remains a major challenge in condensed matter physics. The essential physics lying in two-dimensional copper-oxygen layers is well described by a single-band Hubbard model or its strong-coupling limit t-J model in a two-dimensional square lattice. The recently discovered high-temperature superconductor Ba2CuO3+delta with delta similar to 0.2 has a different crystal structure with a large portion of in-plane oxygen vacancies. We observe that an oxygen vacancy breaks the bond of its two neighboring copper atoms, and propose the ordered vacancies in Ba2CuO3+delta lead to an extended t-J model on an effective brick-wall lattice. For the nearest-neighbor hopping, the brick-wall model can be mapped onto the t-J model on a honeycomb lattice. Our theory explains the superconductivity of Ba2CuO3+delta at a high charge carrier density, and predicts a time-reversal symmetry-broken pairing state.