Cheng Song
The altermagnetic spin splitting torque (SST) was theoretically proposed to combine advantages of conventional spin transfer torque (STT) and spin-orbit torque (SOT) as well as enable controllable spin current [1]. We provide the experimental evidence of SST in collinear antiferromagnet RuO2(100) films. The spin current direction is found to be correlated to the crystal orientation of RuO2 and the spin polarization direction is dependent on (parallel to) the Néel vector [2]. We also observe spin-to-charge conversion arising from the inverse effect of the altermagnetic spin splitting effect in RuO2(101)/Py and RuO2(101)/[Co/Pt] bilayers, based on both spin Seebeck effect. The spin Seebeck voltage can be detected even when the injected spin current is polarized along the directions of either the voltage channel or the thermal gradient, indicating the successful conversion of x- and z-spin polarizations into the charge current. The crystal axes-dependent conversion efficiency further demonstrates that the non-trivial spin-to-charge conversion in RuO2 is ascribed to inverse altermagnetic spin splitting effect, which is distinct from the magnetic/antiferromagnetic inverse spin Hall effects [3]. Also, THz emission signals are greatly enhanced once the inverse altermagnetic spin splitting effect emerges [4]. These findings not only present a new member for the spin torques besides traditional STT and SOT, but also propose RuO2 for both promising spin source and spin sink for spintronics.
[1] R. González-Hernández, et al., Phys. Rev. Lett. 126, 127701 (2021).[2] H. Bai, C. Song, et al. Phys. Rev. Lett. 128, 197202 (2022).
[3] H. Bai, C. Song, et al. Phys. Rev. Lett. (under review)
[4] Y. Liu, C. Song, et al. Adv. Opt. Mater. (under review)