Spin-orbit-entangled electronic structure of Ba$_2$CaOsO$_6$ studied by O $K$-edge resonant inelastic X-ray scattering

TL;DR

This study investigates the electronic structure of Ba$_2$CaOsO$_6$ using RIXS, Raman spectroscopy, and theoretical calculations, revealing a ground state dominated by magnetic octupoles and advancing understanding of spin-orbit physics in complex materials.

Contribution

The paper provides a comprehensive characterization of the local electronic structure and crystal-field symmetry of Ba$_2$CaOsO$_6$, highlighting the role of higher-order multipoles in its ground state.

Findings

No splitting observed in RIXS and Raman spectra, indicating a specific electronic ground state.

Ground state dominated by magnetic octupoles, not dipolar magnetic moments.

Parameters established for future microscopic studies of similar materials.

Abstract

Transition-metal ions with $5d^2$ electronic configuration in a cubic crystal field are prone to have a vanishing dipolar magnetic moment but finite higher-order multipolar moments, and they are expected to exhibit exotic physical properties. Through an investigation using resonant inelastic X-ray spectroscopy (RIXS), Raman spectroscopy, and theoretical ligand-field (LF) multiplet and $ab initio$ calculations, we fully characterized the local electronic structure of Ba$_2$CaOsO$_6$, particularly, the crystal-field symmetry of the 5$d^2$ electrons in this anomalous material. The low-energy multiplet excitations from RIXS at the oxygen $K$ edge and Raman-active phonons both show no splitting. These findings are consistent with the ground state of Os ions dominated by magnetic octupoles. Obtained parameters pave the way for further realistic microscopic studies of this highly unusual class of materials, advancing our understanding of spin-orbit physics in systems with higher-order multipoles.