Quantum anomalous Hall effect and gate-controllable topological phase transition in layered EuCd2As2

While the search for quantum anomalous Hall (QAH) insulators remains active, attention is also being paid to the controllable topological phase transitions, as they could enable the realization of both exotic quantum phenomena and novel spintronic devices. However, stable QAH insulators are innately rare to report since ferromagnetism often accompanies metallicity. Here we identify theoretically the realization of QAH effect in a stable two-dimensional ferromagnetic insulator, ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$ quintuple layers, as evidenced by the analysis of Chern number and chiral edge states. Remarkably, under electric field, a topological phase transition between QAH insulator and quantum spin Hall (QSH) insulator is revealed with the calculated nontrivial spin Chern number and Wannier charge centers for the QSH insulator. Unlike the conventional QSH insulator, here gapless edge states survive even though the time-reversal symmetry is broken by the ferromagnetic ordering. Our findings not only extend the advanced concepts but also afford exciting opportunities for experimental engineering and implementations of magnetic topological states.