Chiral split magnons in metallic g-wave altermagnets: Insights from many-body perturbation theory

Abstract: Altermagnets represent a novel class of magnetic materials that bridge the gap between conventional ferromagnets (FMs) and antiferromagnets (AFMs). Similar to FMs, altermagnets exhibit spin splitting in their electronic bands along specific crystal directions. However, like AFMs, they feature a compensated magnetic structure with zero net magnetic moment. A defining characteristic of altermagnets is the non-degeneracy of their magnon (spin-wave) modes along the crystallographic directions where electronic bands display spin splitting. This non-degeneracy imparts chirality and direction-dependent magnon dispersions, governed by the unique symmetry constraints of altermagnetic systems. In this study, we investigate the interplay between electronic band spin splitting and chiral magnon excitations in a series of metallic g-wave altermagnets ((MZ), where (M)= V, Cr; (Z)= As, Sb, Bi) using the density functional theory and many-body perturbation theory. We systematically analyze the impact of pnictogen substitution (As, Sb, Bi) on spin splitting and magnon dispersions. Our findings reveal pronounced anisotropic magnon band splitting that closely mirrors the spin-split electronic bands. Moreover, we find that magnon damping due to Stoner excitations is highly wavevector-dependent, reaching substantial values in specific Brillouin zone regions. These results highlight the potential of altermagnets for next-generation spintronic and magnonic devices, where direction-dependent magnon lifetimes and nonreciprocal magnon transport could enable new functionalities for chiral magnon propagation and directional magnon control.