Ultrafast electron dynamics in a planar d-wave altermagnet

Altermagnets give rise to novel spin-dependent electron dynamics and transport effects due to their electronic properties, which are intimately related to the symmetries that connect the magnetic sublattices of these materials. In particular, in planar d-wave altermagnets, electronic spin polarizations can be excited in a controlled fashion by linearly polarized optical fields. Experiments using ultrashort optical pulses have shown that these optically created spin polarizations can be detected on a timescale much longer than typical momentum scattering times. The present paper theoretically analyzes the persistence of an optically injected spin polarization by calculating electron-electron and electron-phonon scattering dynamics for the prototypical planar d-wave altermagnetic candidate KRu<inf>4</inf>O<inf>8</inf>. Based on our results, we expect that optical-pulse-generated controlled spin information in any planar d-wave altermagnet is preserved much longer than is possible in typical ferromagnets. Due to its lifetime, such a driven electronic spin polarization may be used as a purely optical identification of the altermagnetic character of a material. © 2025 The Author(s)