Layer number dependence of topological properties in atomically thin films of a ferromagnetic Weyl semimetal Co-based shandite

The kagome ferromagnet Co₃Sn₂S₂ exhibits a giant anomalous Hall effect associated with the Weyl nodes in the band structure [1]. Recently, the quantized anomalous Hall effect in the monolayer was predicted theoretically [2], which awaits experimental realization. However, further investigation is required to clarify the role of lattice structure and magnetism, which are often relevant to the band topology in thin films. In this study, we perform the ab initio calculations for Co-based shandite with one, two, and three Co-kagome-layer films of Sn- and S-end surfaces, with special attention to the optimization of stable lattice structures and magnetic states. We find that, in all the Sn-end films, the ferromagnetic state is stabilized and the gapped Weyl nodes evolve systematically with increasing the number of Co layers, which generates a large anomalous Hall effect. In contrast, the S-end cases show different magnetic states depending on the layer number, which leads to different band topology and transport properties. These results provide a hint for the experimental investigation of the Weyl physics in the thin films of Co-based shandite.

[1] E. Liu et al., Nat. Phys. 14, 1125 (2018).

[2] L. Muechler et al., Phys. Rev. B 101, 115106 (2020).