Spin-orbit-enhanced correlation sensitivity and anomalous magnetic response in non-dimerized 4d4ilmenite CdRuO3.

We report the synthesis and physical properties of CdRuO3, a nominal Ru4+4d4ilmenite with edge-sharing RuO6honeycomb layers. Powder x-ray diffraction establishes a crystallographically non-dimerizedR-3 structure with equivalent Ru-Ru bonds and a strongly distorted RuO6environment. The compacted-pellet resistivity is nonmetallic but non-Arrhenius, while the heat capacity contains a finite residual linear term. Matched nonmagnetic calculations show that PBE+Uwithout spin-orbit coupling remains metallic or semimetallic up toUeff= 3 eV, whereas PBE+SOC+Uexhibits a strongUeffdependence and opens a direct gap of approximately 55 meV at Γ for Ueff= 2.5 eV. Spin-orbit coupling therefore markedly enhances the correlation sensitivity of the non-cubic Ru t2gmanifold. After subtraction of a dilute Curie-Weiss defect contribution, the susceptibility remains weakly nonmonotonic and is inconsistent with both an ordinary Pauli response and independent spin-only S = 1 moments. CdRuO3thus realizes the non-dimerized structural branch predicted for ruthenium ilmenites, but not a simple robust multiorbital metal.