X-ray magnetic circular dichroism in ${\mathrm{RuO}}_2$

We present a numerical simulation of the x-ray magnetic circular dichroism (XMCD) of the $L_{2,3}$ and $M_{2,3}$ edges of Ru in antiferromagnetic ${\mathrm{RuO}}_2$ using a combination of density functional plus dynamical mean-field theory and configuration interaction treatment of the Anderson impurity model. We study the dependence of the dichroic spectra on the orientation of the Néel vector and discuss it in the context of altermagnetism. An approximate equivalence between the XMCD spectra for geometries with x rays propagating parallel and perpendicular to the Néel vector is found and shown to be exact in the absence of valence spin-orbit coupling and a core-valence multipolar interaction.