▎ 摘　　要

A single two-dimensional Dirac cone with a mass gap produces a quantized (spin) Hall step in the absence of magnetic field. What happens in strong electric fields? This question is investigated by analyzing time evolution and dynamics of the spin Hall effect. After switching on a longitudinal electric field, a stationary Hall current is reached through damped oscillations. The Hall conductivity remains quantized as long as the electric field (E) is too weak to induce Landau-Zener transitions, but quantization breaks down for strong fields and the conductivity decreases as 1/root E. These apply to the spin-Hall conductivity of graphene and the Hall and magnetoelectric response of topological insulators.