Cuprate Superconductor

Spin-orbit coupling (SOC) in cuprate superconductors was not a focus of condensed matter research due to the negligible SOC value of the conducting orbitals comparing with the strong electronic correlations and its centrosymmetric crystal structure. By using spin- and angle-resolved photoemission spectroscopy, we unveiled a nontrivial spin-momentum locking pattern in Bi₂Sr₂CaCu₂O_8+x. The asymmetry of the spin-up and spin-down channel suggests the strength of SOC is in the same order of the bilayer interaction. This poses an intriguing question of how the high temperature superconducting state emerges in the presence of SOC.