Doping-induced singlet-to-triplet superconducting transition in Ba2CuO3+δ

In this paper, we perform a numerical simulation on the recently discovered high-temperature superconductor (Tc=73 K) Ba₂CuO3.2 while focusing on doping dependence of alternating CuO₆ octahedra and CuO chainlike states. Employing the multiband random phase approximation, we compute the spin-fluctuation mediated pairing interaction, subsequently determining its pairing eigenvalues and eigenfunctions relative to oxygen-doping levels. We find that, for the certain range of hole doping in Ba₂CuO_3+δ, a singlet d_x²-y²-wave pairing symmetry emerges if we keep the doping below the critical value xc. Interestingly, upon hole doping, the dominant pairing symmetry undergoes a transition to a triplet (odd paring) type from the singlet state. This change in pairing is driven by the competition between the nesting vectors coming from the Fermi surface of d_z² and d_x²-y² orbitals within the CuO₆ octahedra. This triplet state is attainable through hole doping, while suppressing interlayer self-doping effects. Furthermore, we present the density of states within the superconducting phase, offering a potential comparison with tunneling spectra in Ba₂CuO_3+δ. Our research provides insights into the intricate pairing symmetries in Ba₂CuO_3+δ and their underlying pairing mechanisms.