Anisotropic spin stripe domains in bilayer La₃Ni₂O₇

The discovery of superconductivity in La₃Ni₂O₇ under pressure has motivated the investigation of a parent spin density wave (SDW) state, which could provide the underlying pairing interaction. Here, we employ resonant soft x-ray scattering and polarimetry on thin films of bilayer La₃Ni₂O₇ to determine that the magnetic structure of the SDW forms unidirectional diagonal spin stripes with moments lying within the NiO₂ plane and perpendicular to Q_SDW, but without evidence of the strong charge disproportionation typically associated with other nickelates. These stripes form anisotropic domains with shorter correlation lengths perpendicular versus parallel to Q_SDW, revealing nanoscale rotational and translational symmetry breaking analogous to the cuprate and Fe-based superconductors, with possible Bloch-like antiferromagnetic domain walls separating orthogonal domains.