Probing the mesoscopic size limit of quantum anomalous Hall insulators.

The inelastic scattering length (L) is a length scale of fundamental importance in condensed matters due to the relationship between inelastic scattering and quantum dephasing. In quantum anomalous Hall (QAH) materials, the mesoscopic length scale L plays an instrumental role in determining transport properties. Here we examine L in three regimes of the QAH system with distinct transport behaviors: the QAH, quantum critical, and insulating regimes. Although the resistance changes by five orders of magnitude when tuning between these distinct electronic phases, scaling analyses indicate a universal L among all regimes. Finally, mesoscopic scaled devices with sizes on the order of L were fabricated, enabling the direct detection of the value of L in QAH samples. Our results unveil the fundamental length scale that governs the transport behavior of QAH materials.