Critical thickness for the emergence of Weyl features in Co3Sn2S2 thin films

Junya Ikeda,Atsushi Tsukazaki,Koki Takanashi,Kentaro Nomura,Junichi Shiogai,Kohei Fujiwara,Takeshi Seki

doi:10.1038/s43246-021-00122-5

Junya Ikeda, Atsushi Tsukazaki + Show 5 more

Open Access

https://doi.org/10.1038/s43246-021-00122-5

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Abstract

Magnetic Weyl semimetals are quantum phases of matter arising from the interplay of linearly dispersive bands, spin-orbit coupling, and time reversal symmetry breaking. This can be realised, for example, in Co3Sn2S2, based on a cobalt kagome lattice and characterised by intriguing phenomena such as large anomalous Hall effect, Nernst effect, and water oxidation. Here, we attempt to determine the robustness of the twofold necessary conditions for the emergence of the magnetic Weyl semimetal phase in Co3Sn2S2 ultrathin films. Except for two-dimensional layered materials, a reduction of thickness generally makes it difficult to develop topological character and ferromagnetic long-range order. In Co3Sn2S2 films, while ferromagnetic ordering appears robustly even in average thicknesses of one or two unit cells with island-like polycrystalline domains, the anomalous Hall conductivity appears only above a critical thickness of approximately 10 nm. The emergence of surface conduction and large anomalous Hall effect implies the distinct contribution of Weyl nodes and their Berry curvature. These findings reveal an exotic feature of Weyl physics in thin-film based superstructures as well as a potential for future applications in electronic devices.

Highlights

Magnetic Weyl semimetals are quantum phases of matter arising from the interplay of linearly dispersive bands, spin-orbit coupling, and time reversal symmetry breaking
Of proposed magnetic Weyl semimetals[1,2,3,4], particular interest has been focused on Co3Sn2S2 with a kagome lattice of Co5–10, three layers of which are stacked in one unit cell of the crystal structure (Fig. 1a)
While the benefit of the spin-orbit coupling (SOC) is maintained in the ultrathin films, the robustness of the mWSM phase against the thickness reduction is independently influenced by the twofold stability of linear dispersive band and ferromagnetism

Summary

Introduction

Magnetic Weyl semimetals are quantum phases of matter arising from the interplay of linearly dispersive bands, spin-orbit coupling, and time reversal symmetry breaking. This can be realised, for example, in Co3Sn2S2, based on a cobalt kagome lattice and characterised by intriguing phenomena such as large anomalous Hall effect, Nernst effect, and water oxidation. The emergence of surface conduction and large anomalous Hall effect implies the distinct contribution of Weyl nodes and their Berry curvature. Finite contribution of spin-orbit coupling (SOC) produces a gap at the band crossing points except for the protected spatial symmetry positions (from left to centre of Fig. 1b) This is defined as Dirac semimetal (DSM) with possessing helical Fermi arcs (FAs). Island-like polycrystalline domains, the mWSM phase with large anomalous Hall effect (AHE) emerges above a critical thickness of ~10 nm

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