Quantized anomalous Hall resistivity achieved in molecular beam epitaxy-grown MnBi₂Te₄ thin films

The intrinsic magnetic topological insulator MnBi₂Te₄ provides a feasible pathway to the high-temperature quantum anomalous Hall (QAH) effect as well as various novel topological quantum phases. Although quantized transport properties have been observed in exfoliated MnBi₂Te₄ thin flakes, it remains a big challenge to achieve molecular beam epitaxy (MBE)-grown MnBi₂Te₄ thin films even close to the quantized regime. In this work, we report the realization of quantized anomalous Hall resistivity in MBE-grown MnBi₂Te₄ thin films with the chemical potential tuned by both controlled in situ oxygen exposure and top gating. We find that elongated post-annealing obviously elevates the temperature to achieve quantization of the Hall resistivity, but also increases the residual longitudinal resistivity, indicating a picture of high-quality QAH puddles weakly coupled by tunnel barriers. These results help to clarify the puzzles in previous experimental studies on MnBi₂Te₄ and to find a way out of the big difficulty in obtaining MnBi₂Te₄ samples showing quantized transport properties.