Emergence of dxy -wave superconductivity in a doped two-leg diagonal ladder

We propose a doped two-leg spin-$1/2$ diagonal ladder model (or a composite spin model) to simulate a doped spin-1 chain. By using the density matrix renormalization group method for an open chain, we find that the ground state hosts a dominant singlet ${d}_xy$-wave superconducting correlation with features similar to those of the spin-1 Haldane phase. Meanwhile, we apply the renormalized mean-field theory to the model and obtain a ${d}_xy$-wave superconducting state. The superconducting order exhibits a domelike shape as a function of hole concentration $\ensuremath{\delta}$. Our work provides a physical understanding of the origin of ${d}_xy$ pairing symmetry, which originates from antiferromagnetic Heisenberg interaction in the diagonal direction, and the intrachain hopping term makes it stable.