Half-quantized anomalous Hall effect up to 10 K in proximity-coupled topological insulator/ferromagnet van der Waals bilayers

The interplay of magnetism and topological surface states can lead to exotic topological electronic states, such as the quantum anomalous Hall and parity anomaly states. One pathway to create such states is through the magnetic proximity effect at the interface between an insulating ferromagnet and 3D topological insulator, however in previous proximity-coupled samples made using conventional deposition techniques the Hall quantization has been limited to temperatures less than 100 mK. Here, we study bilayers of topological insulator and ferromagnetic insulator made using mechanical exfoliation and stacking techniques instead of deposition. When the Fermi level is within the exchange gap of the topological surface state, the pristine interface created by mechanical stacking allows the anomalous Hall conductivity to achieve the full half-quantized value (e²/2h) associated with the parity anomaly state at temperatures up to 10 K. We also use a chemical-potential sensing technique to make direct measurements of the exchange gap produced by the proximity exchange coupling, finding a value of 10 ± 2 meV at 4.5 K, corroborating the high temperature scale. Our results demonstrate a new strategy for realizing high-temperature magnetic topological states.