Gate-tunable anomalous Hall effect in a 3D topological insulator/2D magnet van der Waals heterostructure*

Experimental demonstrations of strong and controllable interactions between topological insulators and magnets are essential for identifying suitable material platforms that can realize and control topological magneto-electric effects. Here, we demonstrate advantages of samples made by mechanical stacking of exfoliated van der Waals materials for controlling the topological surface state of a three-dimensional topological (TI) insulator via interaction with an adjacent magnet layer. We assemble bilayers with pristine interfaces using exfoliated flakes of the TI BiSbTeSe₂ and the magnet Cr₂Ge₂Te₆, thereby avoiding problems caused by interdiffusion, disorder and spatial inhomogeneities that can affect interfaces made by top-down deposition methods. The samples exhibit an anomalous Hall effect (AHE) with abrupt hysteretic switching. For the first time in samples composed of a TI and a separate ferromagnetic layer, we demonstrate that the amplitude of the AHE can be tuned via gate voltage with a strong peak near the Dirac point. This is the signature expected for the AHE due to Berry curvature associated with an exchange gap induced by interaction between the topological surface state and an out-of-plane-oriented magnet. Our results establish all-vdW exfoliated topological insulator-2D systems as an excellent material platform for manipulating topological surface states and pave the way for improved control of topological magneto-electric effects in TI/magnet heterostructures.