Spin Fluctuations in Quantized Transport of Magnetic Topological Insulators

In magnetic topological insulators, quantized electronic transport is intertwined with spontaneous ordering, as magnetization controls band gaps, hence topology, through the exchange interaction. We show that considering gaps at mean-field level inadequate to predict phase transitions between states of distinct topology. Thermal spin fluctuations disturbing can act frozen disorders strongly scatter electrons, reducing onset temperature appreciably even in absence structural impurities. This effect, which has hitherto been overlooked, provides an alternative explanation recent experiments on insulators.