Quantized anomalous Hall resistivity in epitaxial MnBi₂Te₄ thin films on ultrathin Cr₂Ge₂Te₆ films

MnBi₂Te₄ (MBT), as the first-discovered intrinsic magnetic topological insulator, has emerged as an attractive platform for realizing the high-temperature quantum anomalous Hall (QAH) effect. One approach to elevate the occurring temperature of the QAH effect in an MBT thin film is to introduce neighboring ferromagnetic insulator layers which may reinforce its magnetic order near the surface layers. In this work, we achieved high-quality heterostructures between MBT and ferromagnetic insulator Cr₂Ge₂Te₆ (CGT) thin films with molecular beam epitaxy. By investigating their transport properties at low temperatures, we found that a few-layer CGT buffer layer facilitates high-field quantized transport behavior in MBT films of 3-septuple-layer—the theoretical lower thickness limit of the QAH phase—whereas most early MBT samples, whether thin flakes or epitaxial thin films, become highly insulating at that thickness. These results demonstrate that few-layer CGT serves as an excellent magnetic proximity layer for MBT films, well keeping their intrinsic topological electronic structures and quantized transport properties. CGT/MBT heterostructures thus provide a viable route for exploring high-temperature QAH insulator as well as other novel topological phases in the future.