Observation of spiral spin order and A-phase in Weyl semimetal SmAlSi

The role of Weyl electrons in magnetism has drawn great attention recently. Previous work on NdAlSi [1] has shown a minor spiral modulation of spins, which could be due to nesting between the Weyl nodes; however, a fully spiral order has not been observed. We present evidence of a spiral magnetic order in SmAlSi induced by Weyl-mediated RKKY interactions [2]. We highlight the role of structural symmetries, nesting between the Weyl nodes, and magneto-crysgtalline anisotropy in the spiral magnetic state of SmAlSi. Furthermore, we map the phase diagram, observe a large topological hall effect (THE) within the A-phase, and show that its angle dependence is consistent with the Weyl-mediated DM interactions. Specifically, we show that the angle dependence of THE is consistent with a considerable helical component of the spiral order in SmAlSi as expected from Weyl-mediated RKKY interactions [3].

[1] Gaudet, Jonathan, et al. "Weyl-mediated helical magnetism in NdAlSi." Nature Materials 20, 1650-1656 (2021)

[2] P. Nikolic, Physical Review B 103, 155151 (2021).

[3] X. Yao, J. Gaudet, et al, https://arxiv.org/abs/2206.05121