Fermi-liquid behavior of nonaltermagnetic RuO2

The presence of magnetism in potentially altermagnetic RuO2 has been a subject of intense debate. Using broadband infrared spectroscopy combined with density-functional band-structure calculations, we show that the optical conductivity of RuO2, the bulk probe of its electronic structure, is best described by a nonmagnetic model. The sharp Pauli edge demonstrates the presence of a Dirac nodal line lying 45 meV below the Fermi level. An excellent match between the experimental and plasma frequencies underpins the weakness of electronic correlations. The intraband part of the optical conductivity indicates Fermi-liquid behavior with two distinct scattering rates below 150 K. Fermi-liquid theory also accounts for the temperature-dependent magnetic susceptibility of RuO2 and allows a consistent description of this material as a paramagnetic metal. Published by the American Physical Society 2025