Conical spin order with chiral quadrupole helix in CsCuCl3

TL;DR

This study uses resonant x-ray diffraction to explore complex chiral magnetic and quadrupole orders in CsCuCl3, revealing a novel conical spin structure influenced by spin-orbit interactions.

Contribution

It provides detailed insights into the electric quadrupole moments and complex magnetic modulations in CsCuCl3, highlighting the role of spin-orbit coupling in chiral magnetic systems.

Findings

Identification of electric quadrupole moments around Cu

Discovery of sinusoidal modulations on helical magnetic order

Evidence of significant spin-orbit interaction in Cu2+

Abstract

Here we report a resonant x-ray diffraction (RXD) study at the Cu L3 edge on the multi-chiral 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+.