Chiral magnon splitting in altermagnetic CrSb from first principles

Abstract: Altermagnetism has been proposed as a new type of magnetism, simultaneously exhibiting compensated spin moments in real space and spin-split electronic bands in reciprocal space. Alternating chiral magnon splitting is considered a unique feature of altermagnets. In this work, utilizing linear spin wave theory (LSWT), which is based on a localized spin picture and itinerant time-dependent density functional perturbation theory (TD-DFPT), we investigate the spin fluctuation spectra of altermagnetic CrSb. Along the L-$\Gamma$-L$^{\prime}$ path, the LSWT provides a chiral magnon splitting of up to 9 meV, located at high excitation energies around 140 meV, which is identified to be primarily driven by the splitting of two long-range exchange interactions, with exchange paths along the body diagonal lines of the unit cell. On the other hand, the more realistic TD-DFPT obtains more significant splitting of $\sim$ 30 meV at maximum. However, the splitting is severely smeared out due to strong Landau damping from the Stoner continuum, which may make it difficult to observe experimentally, e.g. through inelastic neutron scattering. We further provide a brief discussion on the connection between the Stoner excitations and the chiral magnon splitting.