Local electronic structure of rutile RuO$_2$

Abstract

Recently, rutile RuO2 has raised interest for its itinerant antiferromagnetism, crystal Hall effect, and strain-induced superconductivity. Understanding and manipulating these properties demands resolving the electronic structure and the relative roles of the rutile crystal field and 4d spin-orbit coupling (SOC). Here, we use O-K and Ru M3 x-ray absorption (XAS) and Ru M3 resonant inelastic x-ray scattering (RIXS) to disentangle the contributions of crystal field, SOC, and electronic correlations in RuO2. The locally orthorhombic site symmetry of the Ru ions introduces significant crystal field contributions beyond the approximate octahedral coordination yielding a crystal field energy scale of ∆(t2g) ≈ 1 eV breaking the degeneracy of the t2g orbitals. This splitting exceeds the Ru SOC (≈ 160 meV) suggesting a more subtle role of SOC, primarily through the modification of itinerant (rather than local) 4d electronic states, ultimately highlighting the importance of the local symmetry in RuO2. Remarkably, our analysis can be extended to other members of the rutile family, thus advancing the comprehension of the interplay among crystal field symmetry, electron correlations, and SOC in transition metal compounds with the rutile structure.

Emerging research landscape of altermagnetism

“…Remarkably, the room-temperature antiparallel magnetic ordering in metallic rutile RuO 2 was discovered [46,47] and investigated [48,49] only recently. The subsequent theoretical and experimental exploration of the T -symmetry breaking macroscopic responses [3, 5, 8, 10-14, 16, 18, 19] has made RuO 2 one of the workhorse materials of the emerging research of altermagnetism.…”