Ab-initio studies of magnetic excitations in RuO2

Abstract:
RuO₂ is a conducting oxide for which colinear antiferromagnetism
persisting up to room temperature has been recently reported in
the rutile phase.

The combined effect of this magnetic order together with crystal
field splitting from the local environment of non-magnetic atoms
makes it an example of altermagnet, where the spin-polarization
of electronic states exhibits a peculiar alternation of split
bands.

Comparable effects can be predicted also in the spectrum of
collective and single-particle magnetic excitations. Working at
the ab-initio level of density functional theory and Green's function
methods, we find that the acoustic magnon branches also appear
energetically non-degenerate over portions of the Brillouin zone.
This appears a consequence of directionality of Heisenberg exchange
interactions beyond the nearest-neighbours. Moving beyond the adiabatic
approximation, we also find that the Landau damping for these
collective excitations also exhibits some peculiar features, which
originate in the alternation of spin-polarization for single-particle
electronic states.
Results can be examined by cross-comparing outcome with and without
altermagnetism, and point toward aspects of possible interest for
further theoretical work, experimental characterization and possible
future technological applications of this type of materials.