Inverse Altermagnetic Spin Splitting Effect-Induced Terahertz Emission in RuO₂

The relativistic inverse spin Hall effect (ISHE) plays a pivotal role in terahertz (THz) emission in magnet/heavy metal bilayers. Here, THz emission from RuO₂/Py bilayers is reported due to not only the relativistic ISHE but also the nonrelativistic inverse altermagnetic spin splitting effect (IASSE) in RuO₂. For the (100)-oriented RuO₂/Py bilayers, the THz emission is greatly enhanced owing to IASSE once the polarization direction of the spin current (from the Py layer induced by pump laser) is parallel to the Néel vector of RuO₂, producing the anisotropic THz emission with twofold symmetry. In contrast, the RuO₂(110)/Py bilayer only exhibits isotropic THz emission because of the absence of IASSE-induced spin-charge conversion in the (110)-oriented RuO₂ films. Apart from the fundamental significance of exploring the IASSE-induced spin-to-charge conversion, the finding also enriches the physical mechanism and modulation method of THz emission in spintronic systems.