Spin and Orbital Magnetism by Light in Rutile Altermagnets

While the understanding of altermagnetism is still at a very early stage, itis expected to play a role in various fields of condensed matter research, forexample spintronics, caloritronics and superconductivity. In the field ofoptical magnetism, it is still unclear to which extent altermagnets as a classcan exhibit a distinct behavior. Here we choose RuO_2, a prototype metallicaltermagnet with a giant spin splitting, and CoF_2, an experimentally knowninsulating altermagnet, to study the light-induced magnetism in rutilealtermagnets from first-principles. We demonstrate that in the non-relativisiclimit the allowed sublattice-resolved orbital response exhibits symmetries,imposed by altermagnetism, which lead to a drastic canting of light-inducedmoments. On the other hand, we find that inclusion of spin-orbit interactionenhances the overall effect drastically, introduces a significant anisotropywith respect to the light polarization and strongly suppresses the canting ofinduced moments. Remarkably, we observe that the moments induced bylinearly-polarized laser pulses in light altermagnets can even exceed inmagnitude those predicted for heavy ferromagnets exposed to circularlypolarized light. By resorting to microscopic tools we interpret our results interms of the altermagnetic spin splittings and of their reciprocal spacedistribution. Based on our findings, we speculate that optical excitations mayprovide a unique tool to switch and probe the magnetic state of rutilealtermagnets.