Enhanced Quantum Anomalous Hall Effect with an Active Capping Layer.

The quantum anomalous Hall effect (QAHE) was discovered a decade ago but is still not utilized beyond a handful of research groups, due to numerous limitations such as extremely low temperature, electric-field-effect gating requirement, small sample sizes, and environmental aging effect. Here, we present a robust platform that provides effective solutions to these problems. Specifically, on this platform, we observe QAH signatures at record-high temperatures, with a Hall conductance of 1.00 e 2 / h at 2.0 K, 0.98 e 2 / h at 4.2 K, and 0.92 e 2 / h at 10 K, on centimeter-scale substrates, without electric-field-effect gating. The key ingredient is an active CrO x capping layer, which substantially boosts the ferromagnetism while suppressing environmental degradation. With this development, QAHE will now be accessible to much broader applications than before.