Why zero-field quantized Hall effects survive only near one kelvin
In plain words
Magnetic topological insulators show a perfectly quantized Hall resistance only at temperatures of order one kelvin, far below the temperature at which they become magnetic, and the reason is debated.
Precise statement
In Cr- or V-doped (Bi,Sb)2Te3 films and odd-layer MnBi2Te4 flakes, full quantum anomalous Hall quantization ($R_{xy} = h/e^2, R_{xx} \to 0$) appears only at $T$ of order 1 K, while magnetic order sets in at 10-30 K and spectroscopic exchange gaps of tens of meV are reported. Identify the mechanism limiting the quantization temperature (magnetic disorder and gap inhomogeneity, antisite defects, surface-gap fluctuations, parallel bulk conduction) and predict how to raise it. An answer quantitatively links measured disorder to the transport activation gap.
What would settle it
Local imaging of the exchange gap correlated with transport activation energies across samples, reproducing the quantization temperature.