Flow of Transport Coefficients in a Film That Shows the Quantum Anomalous Hall Effect. " Trajectory of Anomalous Hall Effect toward the Quantized State in a Ferromagnetic Topological Insulator " , Arxiv: 1406.7450

The observation of the quantum anomalous Hall effect in a ferromagnetic topological insulator, first reported by experimenters in Beijing last year[1], has attracted considerable attention, including a Journal Club Commentary by Leonid Glazman in July 2013. The new e-print by Checkelsky et al. reports experiments by a Japanese group, which further explore the properties of this fascinating system. In addition to confirming general results obtained by the Beijing group, the new work has mapped out the behavior of the longitudinal and Hall conductivities, as a function of temperature and gate voltage, and has found agreement with a picture of a renormalization group flow previously postulated for crossover behavior between quantized Hall states in the familiar integer quantum Hall effect. (See figure, below). This observation is quite interesting, as it is not clear, a priori, why transport properties should be described by such a renormalization group flow in the experimental regime.