The Berry Phase and the Spin Current in AFM Weyl Semimetals
The Weyl semimetal is a new topological state of matter discovered recently. It exhibits not only topologically protected surface states (similar to the topological insulator), but also fascinating charge and spin transport properties in the bulk. In this talk, I will introduce a new type of Weyl semimetal in chiral antiferromagnetic (AFM) materials, Mn3Ge and Mn3Sn . They show Weyl points where bands cross linearly with large Berry phases in the band structure , giving rise to large anomalous Hall effect observed in recent experiments . Furthermore, we have found a unique spin Hall effect (SHE) in these materials , which converts a charge current into a transverse spin current and vice versa. Although the SHE has long been believed to be a phenomenon induced by the spin–orbit coupling, we have proposed an alternative mechanism to realize the SHE without requiring spin-orbit coupling.
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95, 075128 (2017).  Nayak et al. Science Advances 2, 150187 (2016).  Zhang et al. arXiv:1704.03917 (2017).