High-precision realization of robust quantum anomalous Hall state in a hard ferromagnetic topological insulator

An almost ideal quantum anomalous Hall state is observed in (Bi,Sb)Te films doped with vanadium. This state is reached without the application of a polarizing magnetic film, making these materials interesting for low-power electronic applications. The discovery of the quantum Hall (QH) effect led to the realization of a topological electronic state with dissipationless currents circulating in one direction along the edge of a two-dimensional electron layer under a strong magnetic field1,2. The quantum anomalous Hall (QAH) effect shares a similar physical phenomenon to that of the QH effect, whereas its physical origin relies on the intrinsic spin–orbit coupling and ferromagnetism3,4,5,6,7,8,9,10,11,12,13,14,15,16. Here, we report the experimental observation of the QAH state in V-doped (Bi,Sb)2Te3 films with the zero-field longitudinal resistance down to 0.00013 ± 0.00007h/e2 (~3.35 ± 1.76 Ω), Hall conductance reaching 0.9998 ± 0.0006e2/h and the Hall angle becoming as high as 89.993° ± 0.004° at T = 25 mK. A further advantage of this system comes from the fact that it is a hard ferromagnet with a large coercive field (Hc > 1.0 T) and a relative high Curie temperature. This realization of a robust QAH state in hard ferromagnetic topological insulators (FMTIs) is a major step towards dissipationless electronic applications in the absence of external fields.