Spin-Splitting Magnetoresistance in Altermagnetic RuO₂ Thin Films

The recently discovered altermagnets, featured by the exotic correlation of magnetic exchange interaction and alternating crystal environments, have offered exciting cutting-edge opportunities for spintronics. Nevertheless, the altermagnetism of RuO₂, one of the earliest-discovered altermagnets, is currently under intense debate. Here, this controversy is attempted to be resolved by demonstrating a spin-splitting magnetoresistance (SSMR) effect that is driven by a spin current associated with the giant nonrelativistic spin splitting of an altermagnet. Compared to the spin Hall magnetoresistance induced by a conventional relativistic spin current, the SSMR is characterized by unusual angular dependence with a phase-shift feature underpinned by the Néel-vector orientation and pronounced temperature dependence caused by its susceptibility to electron scattering. Through systematical investigations on the magnetoresistance of (101)-RuO₂/Co bilayers, a sizable SSMR is disentangled and hence a Néel vector along [001] direction is unveiled. This work not only demonstrates a simple electric avenue for probing the Néel vector of altermagnets, but also indicates long-range magnetic order in thin films of RuO₂.