  The experimental observation of the long-sought quantum anomalous Hall effect
was recently reported in magnetically doped topological insulator thin films
[Chang et al., Science 340, 167 (2013)]. An intriguing observation is a rapid
decrease from the quantized plateau in the Hall conductance, accompanied by a
peak in the longitudinal conductance as a function of the gate voltage. Here,
we present a quantum transport theory with an effective model for magnetic
topological insulator thin films. The good agreement between theory and
experiment reveals that the measured transport originates from a topologically
nontrivial conduction band which, near its band edge, has concentrated Berry
curvature and a local maximum in group velocity. The indispensable roles of the
broken structure inversion and particle-hole symmetries are also revealed. The
results are instructive for future experiments and transport studies based on
first-principles calculations.
