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Quantum anomalous Hall effect (QAHE) in magnetic ion-doped topological insulators (TIs) has been actively researched with great attention by virtue of its fascinating phenomena of quantized Hall conductance at zero external magnetic field. Even though various approaches have been reported so far to increase the QAHE temperature, the observable temperature of the QAHE has been limited below 500 mK without the help of gating.   

In this presentation, we investigate the QAHE with various capping materials in multilayer magnetic TIs. As a platform, we employed a trilayer Cr-doped (Bi, Sb)₂Te₃ structure with heavy Cr doping at outer (top and bottom) layers. In a very thin Cr-capped sample with optimized Bi, Cr doping, we observe the fully quantized value at 2 K without the external electric field for gating. This development will allow QAHE to be accessible to a wider range of probes that have been beyond reach for QAH studies due to temperature and other limiting requirements so far.