Interlayer Coupling Induced Plateau Phase Transition in Quantum Anomalous Hall Insulators*

Recently, the high Chern number quantum anomalous Hall (QAH) effect has been realized in magnetic topological insulator(TI)/TI multilayers. In this work, we employed molecular beam epitaxy (MBE) to fabricate a series of magnetic TI/TI penta-layer heterostructures, specifically 3 quintuple layers (QL) (Bi, Sb)_1.73Cr_0.27Te₃/4QL (Bi, Sb)₂Te₃/d QL (Bi, Sb)_1.73Cr_0.27Te₃/4 QL (Bi, Sb)₂Te₃ /3 QL (Bi, Sb)_1.73Cr_0.27Te₃, by systematically altering the thickness d of the middle magnetic TI layer. By performing electrical transport measurements, we observed a zero magnetic field quantum phase transition between C = 1 and C = 2 QAH states.  For d ≤ 1, the sample exhibits the well-quantized C = 1 QAH state. For d ≥ 2, the sample exhibits the well-quantized C = 2 QAH state. However, for 1 ≤  d ≤ 2, we observed a monotonic reduction in Hall resistance from h/e² to h/2e², with a concomitant peak in the longitudinal resistance. The quantum phase transition driven by changes in the Chern number is attributed to the interlayer coupling between the upper and lower undoped TI layers, where two C= 1 QAH states emerge.