Magnetic Topological Insulator Heterostructures: From Axion Physics to the Topological Hall Effect

Topological insulator is a material in which the interior is insulating but wherein the electrons travel without resistance along surface/edge conducting channels. The nontrivial Dirac surface/edge states of a TI are induced by intrinsic strong spin-orbit coupling and protected by time-reversal symmetry (TRS). Breaking the TRS of a TI with magnetic doping can lead to many exotic topological quantum phenomena such as the quantum anomalous Hall (QAH) effect [1]. The QAH effect has been experimentally demonstrated in magnetic TI thin films, specifically Cr- and/or V- doped (Bi,Sb)₂Te₃ [2]. Recently, we fabricated magnetic TI based sandwich heterostructures wherein two TI films doped with the same or different magnetic ions are sandwiched by an undoped TI layer. The undoped TI layer serves as a spacer to decouple the exchange interaction between the two magnetic TI layers, thus the magnetization in each magnetic TI layer can be treated independently. In heterostructures with different magnetic TI layers, we realized a zero Hall conductance plateau in the antiparallel magnetization alignment region, which is a realization of the axion insulator state. This observation provides a promising platform for the exploration of axion electrodynamic physics [3]. In heterostructures with the same magnetic doping, we observed a crossover from the QAH to topological Hall (TH) effects. The combination of QAH and TH effects in a single sample facilitates the study of the interplay of momentum-space and real-space Berry curvatures in magneto-transport phenomena [4].
[1] R. Yu et al, Science 329, 61 (2010).
[2] C. Z. Chang et al., Science 340, 167 (2013); Nat. Mater. 14, 473 (2015).
[3] D. Xiao et al., PRL 120, 056801 (2018).
[4] J. Jiang et al, submitted (2018).