Spin- to charge-current conversion in altermagnetic candidate RuO 2 probed by terahertz emission spectroscopy

Using the THz emission spectroscopy, we investigate ultrafast spin-to-charge current conversion in epitaxial thin films of the altermagnetic candidate RuO2. We perform a quantitative analysis of competing effects that can contribute to the measured anisotropic THz emission. These include the anisotropic inverse spin splitter and spin Hall effects in RuO2, the anisotropic conductivity of RuO2, and the birefringence of the TiO2 substrate. We observe that the leading contribution to the measured signals comes from the anisotropic inverse spin Hall effect, with an average spin-Hall angle of 2.4×10−3 at room temperature. In comparison, a possible contribution from the altermagnetic inverse spin-splitter effect is found to be approximately 2–4×10−4. Our work stresses the importance of carefully disentangling spin-dependent phenomena that can be generated by the unconventional altermagnetic order, from the effects of the relativistic spin-orbit coupling.