Exploring Osmium and Ruthenium Oxides: Altermagnetism in Rutiles and Phonons in Sparse Matter

This work presents a comprehensive investigation of two distinct classes of osmium and ruthenium oxides, OsO₂-RuO₂ and OsO₄-RuO₄, revealing insights into their structural, electronic, and vibrational behaviors. OsO₂ and RuO₂, belonging to the rutile family, are analyzed in terms of their electronic structure, demonstrating antiferromagnetism and spin-splitting driven by crystal symmetry—a hallmark of altermagnetism. Notably, OsO₂ exhibits reduced Fermi velocities relative to RuO₂, suggesting limited charge mobility but potential stability for spintronic applications. Phonon density of states (PDOS) measurements of RuO₂ via neutron scattering further confirm the accuracy of our computational predictions of vibrational behavior.

In contrast, non-magnetic OsO₄ and RuO₄ compounds feature unique molecular tetrameric structures with rare +8 oxidation states. Modeling these sparse molecular materials requires van der Waals (vdW)-corrected density functional theory (DFT) to capture weak inter-tetramer interactions. Our results show that vdW corrections significantly reduce structural volume errors and stabilize soft phonon modes. Experimental PDOS data for OsO₄ further validates these computational findings. Together, these studies on OsO₂-RuO₂ and OsO₄-RuO₄ establish a cohesive framework for understanding the interplay between electronic structure, lattice dynamics, and material stability across different oxidation states, offering new benchmarks for altermagnetic systems and vdW-corrected DFT methods.