Oxygen-driven altermagnetic symmetry inducing d-wave superconductivity in the cuprates and nickelates

Since the discovery of cuprate high-Tc superconductivity, numerous theoretical frameworks have been proposed to explain its mechanism; Anderson's RVB picture [Science 235, 1196-1198, 1987] and U(1) gauge theory [Phys. Rev. Lett. 76, 503-506, 1996] motivate a minimal one-band view that largely integrates out oxygen. By contrast, altermagnetism [Phys. Rev. X 12, 040501, 2022] yields a d-wave-like k-space magnetic texture from alternatingly rotated nonmagnetic cages; La2CuO4 (the parent of a high-Tc cuprate) is a prototypical example. As a proof of principle, we show in La2CuO4 that an alternating local pairing potential on the two Cu sublattices (plus/minus s(r)) produces a nodal, d-wave-like Delta(k). As orthorhombic tilts are, however, not the driver (and even suppress superconductivity in nickelates; [Nature 621, 493, (2023)], we then show that the in-plane oxygen sublattice of CuO2/NiO2 layers, ubiquitous in cuprates and nickelates, intrinsically realizes the same symmetry. Imposing an oxygen-centered, staggered s pairing yields a d-wave gap with perfect C4 symmetry, demonstrated self-consistently in NdNiO2 from first principles. While the underlying mechanism that drives this order is unclear, we outline possible origins. Further, this description of superconductivity enables mapping a real-space superconducting order parameter onto a lattice picture, allowing superconductivity and Hubbard physics to be treated on the same footing.