The quantum anomalous Hall effect is a phenomenon in which certain magnetic insulators exhibit a zero-field Hall resistance value, 𝑅 𝐻, that is precisely quantized in terms of fundamental constants of nature: 𝑅 𝐻 = ℎ/𝑛𝑒 2, where ℎ is Planck's constant, 𝑒 is the charge of the electron and 𝑛 is a