High-order Dy multipole motifs observed in DyB₂C₂ with resonant soft x-ray Bragg diffraction

Resonant soft x-ray Bragg diffraction at the Dy M_4,5 edges has been exploited to study Dy multipole motifs in DyB₂C₂. Our results are explained by introducing the intra-atomic quadrupolar interaction between the core 3d and valence 4f shell. This allows us to determine for the first time higher-order multipole moments of dysprosium 4f electrons and to draw their precise charge density. The Dy hexadecapole and hexacontatetrapole moment have been estimated at -20% and +30% of the quadrupolar moment, respectively. No evidence for the lock-in of the orbitals at T_N has been observed, in contrast to earlier suggestions. The multipolar interaction and the structural transition cooperate along c but they compete in the basal plane, explaining the canted structure along [110].