Mapping the phase diagram of the quantum anomalous Hall and topological Hall effects in a dual-gated magnetic topological insulator heterostructure

Abstract

We use magnetotransport in dual-gated magnetic topological insulator heterostructures to map out a phase diagram of the topological Hall and quantum anomalous Hall effects as a function of the chemical potential (primarily determined by the back gate voltage) and the asymmetric potential (primarily determined by the top gate voltage). A theoretical model that includes both surface states and valence band quantum well states allows the evaluation of the variation of the Dzyaloshinskii-Moriya interaction and carrier density with gate voltages. The qualitative agreement between experiment and theory provides strong evidence for the existence of a topological Hall effect in the system studied, opening up a new route for understanding and manipulating chiral magnetic spin textures in real space. In recent years, condensed matter physics has seen a growing interest in studying the interplay between topology in momentum space and topology in real space. The former often manifests in nontrivial band structures in momentum space arising from the combined effects of some fundamental symmetry and strong spin-orbit coupling, while the latter (also a product of spin-orbit coupling) is associated with chiral magnetic spin textures in real space [1–3]. The quantum anomalous Hall (QAH) effect [4–12], induced by a non-trivial Berry curvature in a topological system with broken time-reversal symmetry, provides convincing evidence of topology in momentum space. It is characterized by a quantized Hall resistance and a vanishing longitudinal resistance at zero magnetic field and has been realized in magnetically doped topological insulators (TIs) [8–12]. The topological Hall effect (THE), induced by the interaction of itinerant charge carriers with chiral spin textures such as magnetic skyrmions or chiral domain walls, is regarded as a signature of topology in real space [3]. The THE manifests as an excess Hall voltage superimposed on the usual hysteretic anomalous Hall voltage that arises in magnetic conductors. Such a signature has been observed and interpreted as evidence for the THE in many systems, including MnSi [13, 14], MnGe [15], FeGe [16], SrIrO3/SrRuO3 interface [17, 18], magnetically doped TI heterostructures [19–21], and TI/BaFe12O19 heterostructures [22]. Given this context, it is valuable to identify model systems wherein the QAH and THE can be systematically studied as a function of some easily tuned system parameters. We recently studied the THE in one such model system, TI sandwich heterostructures of (Cr0.15(Bi,Sb)1.85Te3 (Bi,Sb)2Te3 ∗ Corresponding authors: [email protected], [email protected]