by resonant elastic x-ray scattering*

The simple, rutile oxide, RuO₂, is the parent material of the perovskite ruthenates and a source of current intrigue following the surprising discoveries of antiferromagnetism [1, 2], and strain-induced superconductivity [3] in this material. The details of the magnetic structure and its relationship to the novel superconducting phase, however, remain open questions. Recent magnetic resonant scattering results from the highly-strained, superconducting films deviate from those in bulk RuO₂ [4], and simulations of resonant diffraction from several antiferromagnetic motifs have led some researchers to question the evidence for collinear antiferromagnetism in RuO₂ [5]. These critics instead suggest a “chiral signature,” measured with circularly-polarized, resonant x-rays, as an unambiguous indicator of long-range magnetic order. Here we present the results of such an experiment, exploiting both circular and linear polarization analysis, to conclusively determine the magnetic structure of RuO₂. We report findings from a set of superconducting thin films grown by molecular beam epitaxy, ranging from relaxed and bulk-like to ultrathin and coherently strained. 

[1] Berlijn T. et al, Phys. Rev. Lett. 118, 2 (2017).

[2] Zhu, Z. H. et al , Phys. Rev. Lett. 122, 17202 (2019).

[3] Ruf, J. P. et al, Nat. Commun. 12, 59 (2021).

[4] Gregory B. Z. et al, arXiv:2201.07297 (2022).

[5] Lovesey, S. W. et al, Phys. Rev. B 105, 1 (2022).