Evidence for Octupole Order in Ce$_{0.7}$La$_{0.3}$B$_6$ from Resonant X-ray Scattering

TL;DR

This study provides theoretical evidence that the phase IV of Ce$_{0.7}$La$_{0.3}$B$_6$ exhibits Gamma_{5u}-type octupole order, confirmed through analysis of azimuthal angle dependence in resonant X-ray scattering.

Contribution

The paper demonstrates that the observed azimuthal angle dependence in resonant X-ray scattering uniquely supports Gamma_{5u}-type octupole order in Ce$_{0.7}$La$_{0.3}$B$_6$, excluding other order parameters.

Findings

Azimuthal angle dependence matches Gamma_{5u}-type octupole order.

Calculation reproduces experimental data for multiple polarizations.

Other order parameters are ruled out based on symmetry analysis.

Abstract

The azimuthal angle dependence observed in the resonant X-ray scattering in phase IV of Ce$_{0.7}$La$_{0.3}$B$_6$ is analyzed theoretically. It is shown that the peculiar angle dependence observed in the E2 channel is consistent with the Gamma_{5u}-type octupole order with principal axis along (111) and equivalent directions. Under the assumption that the four equivalent octupole domains are nearly equally populated in the sample, the observed angle dependences are reproduced by calculation for both sigma-sigma' and sigma-pi' polarizations. The calculation for various symmetries of order parameters excludes unambiguously other order parameters than the Gamma_{5u}-type octupole.