Interlayer coupling induced quantum phase transition in quantum anomalous Hall multilayers

A quantum phase transition arises from competition between different ground states and is typically accessed by varying a single physical parameter near absolute zero temperature. The quantum anomalous Hall (QAH) effect with high Chern number C has recently been achieved in magnetic topological insulator (TI) multilayers. In this work, we employ molecular beam epitaxy to synthesize a series of magnetic TI pentalayers by varying the thickness of the middle magnetic TI layer, designated as m quintuple layers. Electrical transport measurements demonstrate a quantum phase transition between the C=1 and C=2 QAH states. For m≤1 and m≥2, the sample exhibits the well-quantized C=1 and C=2 QAH states, respectively. For 1<m<2, we observe a monotonic decrease in Hall resistance from h/e2 to h/2e2 with increasing m, accompanied by a peak in the longitudinal resistance. The quantum phase transition between the C=1 and C=2 QAH states is attributed to the weakening of the interlayer coupling between the top and bottom C=1 QAH layers. Our findings provide a scalable strategy for engineering QAH devices with a tunable Chern number. This approach enables precise control and enhanced functionality in chiral edge current based electronic devices.