Theoretical Evidence for the Berry-Phase Mechanism of Anomalous Hall Transport: First-principles Studies on CuCr${}_2$Se${}_{4-x}$Br${}_x$

To justify the origin of anomalous Hall effect (AHE), it is highly desirable to have the system parameters tuned continuously. By quantitative calculations, we show that the doping dependent sign reversal in CuCr${}_2$Se${}_{4-x}$Br${}_x$, observed but not understood, is nothing but direct evidence for the Berry-Phase mechanism of AHE. The systematic calculations well explain the experiment data for the whole doping range where the impurity scattering rates is changed by several orders with Br substitution. Further sign change is also predicted, which may be tested by future experiments.