Theory of spin/charge transport and magnetic orderings in stacked kagome-lattice Weyl semimetal*

Weyl semimetals are zerogap semiconductors with relativistic linear dispersion near the Fermi level. In particular, magnetic Weyl semimetals, in which time-reversal symmetry is broken by magnetism, exhibit an anomalous Hall effect. Co₃Sn₂S₂ (CSS) is a stacked kagome lattice system that is a candidate material  for magnetic Weyl semimetals. CSS shows an out-of-plane ferromagnetic ordering  and a giant intrinsic anomalous Hall effect originated from the Berry curvature generated by the Weyl points. On the other hand, it has been reported experimentally that carrier-doped  systems show changes in magnetic structure such as suppression of out-of-plane magnetic moments. However, theoretical investigations on the magnetic orderings in the case of different electron numbers are still needed. Furthermore, in systems with strong spin-orbit coupling such as CSS, transport phenomena such as anomalous/spin Hall effects are expected to correlate with magnetic orderings.

In this talk, we  introduce our recent analyses of magnetic ordering and spin/charge transport using the CSS effective tight-binding model. This model is a two-orbital dp model using the d orbital of Co and the p orbital of Sn, and reproduces the structure of the Weyl points and density of states near the Fermi level obtained by first-principles calculations. When the electron-electron interaction is introduced within the mean-field approximation, various magnetic orderings (paramagnetic,  ferromagnetic, and antiferromagnetic) arise by changing the number of electrons. In particular, in the antiferromagnetic state, although the net magnetization is zero,  the anomalous Hall conductivity and orbital magnetization are finite. Finally, we discuss connections between  magnetic orderings and the intrinsic spin Hall effect.