Time-resolved ultrafast oscillation of octupole polarization in a chiral antiferromagnet Mn₃Sn

Understanding of spin-precession dynamics forms the basis of spintronic application. For the ultrafast THz control of staggered moments in antiferromagnets, the time-resolved observation of spin precession is essential for developing the associated technology. However, such observation has been limited to insulators to date [1]. Recently, the metallic antiferromagnets Mn₃X have attracted significant attention for its strong response (e.g. anomalous Hall effect) comparable to ferromagnets owing to the hidden ferroic order, which configures large Berry curvature originated from Weyl points in momentum space [2]. Such ferroic order can be characterized by cluster octupoles based on neighboring magnetic moments [3], and thus it is highly important to clarify the dynamics of cluster octupole for designing the spintronic application.
In this talk, we report our time-resolved observation of spin precession in a metallic chiral antiferromagnet Mn₃Sn [4]. In particular, we find that the dynamics of the cluster octupole is enhanced by exchange interaction, and it is feasible to conduct an ultrafast switching at < 10 ps, a hundred times faster than the case of spin-magnetization in a ferromagnet. Moreover, our theoretical study demonstrates that the domain wall velocity of the cluster octupole could reach as high as 10 km/s. Our work paves the path towards realizing ultrafast electronic devices.
[1] P. Němec et al., Nat. Phys. 14, 229 (2018).
[2] S. Nakatsuji et al., Nature 527, 212 (2015).
[3] M.-T. Suzuki et al., Phys. Rev. B 95, 094406 (2017).
[4] S. Miwa et al., submitted.