Suppressing metallicity of topological insulator GdBi thin films by quantum confinement

GdBi is an antiferromagnetic semimetal which has been proposed to have non-trivial band topology.[1,2] Despite attempts to experimentally observe its topological nature, it is challenging due to the large band overlap between the conduction and valence bands. Here we show via electrical transport measurements that quantum confinement can suppress the band overlap in GdBi thin films. The semimetallicity is lifted below a film thickness of approximately 8 crystallographic unit cells while the antiferromagnetic order is preserved down to our minimum thickness of 5 crystallographic unit cells. This is a step toward realizing a bulk insulating antiferromagnetic topological insulator, which can potentially realize a Chern insulating state in the monolayer limit.
[1] M. Zeng and C. Fang et al., arXiv:1504.03492 (2015). [2] X. Duan et al., arXiv:1802.04554 (2018).