Coexistence of Quantum Hall and Quantum Anomalous Hall Phases in Disordered MnBi2Te4

In most cases, to observe quantized Hall plateaus, an external magnetic field is applied in intrinsic magnetic topological insulators MnBi2Te4. Nevertheless, whether the nonzero Chern number (C not equal 0) phase is a quantum anomalous Hall (QAH) state, or a quantum Hall (QH) state, or a mixing state of both is still a puzzle, especially for the recently observed C = 2 phase [Deng et al., Science 367, 895 (2020)]. In this Letter, we propose a physical picture based on the Anderson localization to understand the observed Hall plateaus in disordered MnBi2Te4. Rather good consistency between the experimental and numerical results confirms that the bulk states are localized in the absence of a magnetic field and a QAH edge state emerges with C = 1. However, under a strong magnetic field, the lowest Landau band formed with the localized bulk states, survives disorder, together with the QAH edge state, leading to a C = 2 phase. Eventually, we present a phase diagram of a disordered MnBi2Te4 which indicates more coexistence states of QAH and QH to be verified by future experiments.