t-J model on the effective brick-wall lattice for the recently discovered high-temperature superconductor Ba$_2$CuO$_{3+\delta}$

TL;DR

This paper models the high-temperature superconductor Ba$_2$CuO$_{3+eta}$ using an extended t-J model on an effective brick-wall lattice, explaining its superconductivity and predicting a time-reversal symmetry breaking pairing state.

Contribution

It introduces a novel effective lattice model for Ba$_2$CuO$_{3+eta}$ considering oxygen vacancies, linking it to a brick-wall lattice and predicting new superconducting pairing symmetry.

Findings

The brick-wall lattice model maps onto a honeycomb lattice t-J model.

The theory explains high charge carrier density superconductivity.

It predicts a time-reversal symmetry broken pairing state.

Abstract

Layered copper oxides have highest superconducting transition temperatures at ambient pressure. Its mechanism remains a grand challenge in condensed matter physics. The essential physics lying in 2-dimensional copper-oxygen layers is well described by a single band Hubbard model or its strong coupling limit t-J model in 2-dimensional square lattice. Recently discovered high temperature superconductor Ba$_2$CuO$_{3+\delta}$ with $\delta \sim 0.2$ has different crystal structure with large portion of in-plane oxygen vacancies. We observe that an oxygen vacancy breaks the bond of its two neighboring copper atoms, and propose ordered vacancies in Ba$_2$CuO$_{3+\delta}$ lead to extended t-J model on an effective brick-wall lattice. For the nearest neighbor hopping, the brick-wall model can be mapped onto t-J model on honeycomb lattice. Our theory explains the superconductivity of Ba$_2$CuO$_{3+\delta}$ at high charge carrier density, and predict a time reversal symmetry broken pairing state.