We demonstrate advantages of samples made by mechanical stacking of exfoliated van der Waals materials for controlling the topological surface state of a 3-dimensional topological insulator (TI) via interaction with an adjacent magnet layer 1. We assemble bilayers with pristine interfaces using exfoliated flakes of the TI BiSbTeSe2 and the magnet Cr2Ge2Te6 (Fig. 1), thereby avoiding problems caused by interdiffusion that can affect interfaces made by top-down deposition methods. The samples exhibit an anomalous Hall effect with abrupt hysteretic switching (Fig. 2a). For the first time in samples composed of a TI and a separate ferromagnetic layer, we demonstrate that the amplitude of the anomalous Hall effect can be tuned via gate voltage with a strong peak near the Dirac point (Fig. 2b). This is the signature expected for the anomalous Hall effect due to Berry curvature associated with an exchange gap induced by interaction between the topological surface state and an out-of-plane-oriented magnet 2. Our results demonstrate the advantages of a clean all-vdW exfoliated topological insulator-2D magnet system for manipulating topological surface states, and pave the way for improved control of topological magneto-electric effects in TI/magnet heterostructures.

References 1 V Gupta, R Jain, Y Ren et al., arXiv preprint arXiv:2206.02537 (2022). 2 D. Xiao, M. C. Chang & Q. Niu, Rev. Mod. Phys. 82, 1959 (2010).