Anisotropic Spin Stripe Domains in Bilayer La$_3$Ni$_2$O$_7$

TL;DR

This paper reveals that bilayer La$_3$Ni$_2$O$_7$ hosts anisotropic unidirectional spin stripe domains with in-plane moments, providing insights into its magnetic structure relevant to its superconductivity under pressure.

Contribution

The study uncovers the anisotropic spin stripe magnetic structure in La$_3$Ni$_2$O$_7$, showing unidirectional diagonal SDW domains without charge disproportionation, advancing understanding of its magnetic properties.

Findings

Unidirectional diagonal spin density wave with in-plane moments.

Anisotropic domains with different correlation lengths.

Nanoscale symmetry breaking similar to cuprates and Fe-based superconductors.

Abstract

The discovery of superconductivity in La$_3$Ni$_2$O$_7$ 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 La$_3$Ni$_2$O$_7$ to determine that the magnetic structure of the SDW forms unidirectional diagonal spin stripes with moments lying within the NiO$_2$ plane and perpendicular to $\mathbf{Q}_{SDW}$, 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 $\mathbf{Q}_{SDW}$, 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.