Revealing hidden magnetoelectric multipoles using Compton scattering

Abstract

Magnetoelectric multipoles, which are odd under both space-inversion I and time-reversal T symmetries, are fundamental in understanding and characterizing magnetoelectric materials. However, the detection of these magnetoelectric multipoles is often not straightforward as they remain “hidden” in conventional experiments in part since many magnetoelectrics exhibit combined IT symmetry. In this paper, we show that the antisymmetric Compton profile is a unique signature for all the magnetoelectric multipoles, since the asymmetric magnetization density of the magnetoelectric multipoles couples to space via spin-orbit coupling, resulting in an antisymmetric Compton profile. We develop the key physics of the antisymmetric Compton scattering using symmetry analysis and demonstrate it using explicit first-principles calculations for two well-known representative materials with magnetoelectric multipoles, insulating LiNiPO_{4} and metallic Mn_{2}Au. Our work emphasizes the crucial roles of the orientation of the spin moments, the spin-orbit coupling, and the band structure in generating the antisymmetric Compton profile in magnetoelectric materials.