Effects of spin-flip scattering on gapped Dirac fermions

We investigate the effects of spin-flip scattering on the Hall transport and the spectral properties of gapped Dirac fermions. We find that in the weak scattering regime, the Berry curvature distribution is dramatically compressed in the electronic energy spectrum, becoming singular at band edges. As a result, the Hall conductivity has a sudden jump (or drop) of e²/(2h) when the Fermi energy sweeps across the band edges, and otherwise is a constant quantized in units of e²/(2h). The spectral properties such as the density of states and the spin polarization are also greatly enhanced near band edges. Possible experimental methods to detect these effects are discussed.