2025/06/23 by Ruairidh Sutcliffe, K. H. Hart, Sutcliffe, Ruairidh +6 · 3 citations
Physics and Astronomy · #Topological Materials and Phenomena #Advanced Condensed Matter Physics #Rare-earth and actinide compounds
paper · pdf · doi:10.1103/n11w-csdh
Motivated by the recent discovery of anomalously large magnetic response of chiral phonons in dipolar magnets, we explore an extension to study Einstein quantum phonon modes coupled to multipolar moments. We consider the case of non-Kramers Γ3 doublets which encapsulate quadrupolar and Ising octupolar degrees of freedom, and which feature a symmetry-allowed linear coupling between local quadrupolar moments and Raman active Eg phonon modes (dx2-y2,d3z2-r2). We show that either octupolar or quadrupolar ordering leads to degeneracy breaking of the Eg phonon doublet, with ferro-octupolar order favoring pseudo-chiral phonon eigenmodes with a detectable energy splitting. We describe this physics using a path integral approach in the limit where `fast' phonon modes sense the `slow' pseudospins as a static background which we average over using Monte Carlo simulations. We discuss implications for materials such as Ba2CaOsO6 and PrV2Al20 where Raman spectroscopy of phonons could be used as a potential probe of hidden octupolar order. Our work extends the important concept of chiral phonons to a large class of multipolar magnets.