Conical spin order with chiral quadrupole helix in CsCuCl3

Here we report a resonant x-ray diffraction (RXD) study at the Cu L3 edge on the multichiral system CsCuCl3, exhibiting helical magnetic order in a chiral crystal structure. RXD is a powerful technique to disentangle electronic degrees of freedom due to its sensitivity to electric monopoles (charge), magnetic dipoles (spin), and electric quadrupoles (orbital). We characterize electric quadrupole moments around Cu ascribed to the unoccupied Cu 3d orbital, whose quantization axis is off the basal plane. Detailed investigation of magnetic reflections reveals additional sinusoidal modulations along the principal axis superimposed on the reported helical structure, i.e., a longitudinal conical (helical-butterfly) structure. The out-of-plane modulations imply significant spin-orbit interaction despite S = 1/2 of Cu2+.

Automated summary

In this study, resonant x-ray diffraction (RXD) was used to investigate helical magnetic order in the multichiral system CsCuCl3, revealing electric quadrupole moments around Cu. The detailed investigation also uncovered additional sinusoidal modulations known as longitudinal conical structure superimposed on the reported helical structure. These findings suggest significant spin-orbit interaction despite the presence of Cu2+ with S = 1/2.