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 field 1 , 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 ferromagnetism 3 , 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) 2 Te 3 films with the zero-field longitudinal resistance down to 0.00013 ± 0.00007 h / e 2 (~3.35 ± 1.76 Ω), Hall conductance reaching 0.9998 ± 0.0006 e 2 / 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 ( H c > 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.