Abstract
By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. Further breaking of inversion symmetry is possible by employing magnetic topological insulator heterostructures that host non-degenerate top and bottom surface states. Here we demonstrate the tailored-material approach for the realization of robust quantum Hall states in the bilayer system, in which the cooperative or cancelling combination of the anomalous and ordinary Hall responses from the respective magnetic and non-magnetic layers is exemplified. The appearance of quantum Hall states at filling factor 0 and +1 can be understood by the relationship of energy band diagrams for the two independent surface states. The designable heterostructures of magnetic topological insulator may explore a new arena for intriguing topological transport and functionality.
Highlights
By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap
We fabricated topological insulator (TI) bilayer heterostructures composed of Crx(Bi1 À ySby)[2] À xTe3 (CBST) and (Bi1 À ySby)2Te3 (BST) on semi-insulating InP(111) substrates using molecular-beam epitaxy (MBE; see Supplementary Fig. 1 and Supplementary Note 1 for energy-dispersive X-ray spectroscopy mapping images of elements taken with a scanning transmission electron microscope), as schematically illustrated in Fig. 1a,c
We confirm that neither quantum Hall effect (QHE) nor quantum anomalous Hall effect (QAHE) is observed in single layer films of 5-nm BST and 2-nm Crx(Bi1 À ySby)2 À xTe3 (CBST), implying no surface Dirac states formed due to hybridization between two surfaces in thin single layers
Summary
By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. When the time-reversal symmetry is broken with applying enough high magnetic fields or introducing spontaneous magnetization by doping magnetic impurities in 3D-TI, quantum Hall effect (QHE) or quantum anomalous Hall effect (QAHE) emerges as the hallmark of emergent states of two-dimensional electron system[5]. In the semi-magnetic TI bilayer, we can expect that the both magnetization M and magnetic field B identically drive the surface Dirac states in each TI layer to the QH states, which can be regarded as a hybrid phenomenon of QAHE in magnetic TI and QHE in non-magnetic TI layers with the common edge state. The confinement of magnetic ions in a limited region of the heterostructure may suppress the disorder on the whole sample
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