Impurity effects and bandgap closing in massive Dirac systems

We investigate the effects in the spectral properties of a massive Dirac system of the dynamical renormalization induced by disorder/impurity scattering within the self-consistent Born approximation. We show how these effects lead to a remarkable closing of the bandgap edge. Above a critical value Uc of the impurity scattering the gap eventually closes, giving rise to a finite density of states at zero energy. We show that the bandgap closing stems from the quasiparticle dynamical renormalization, and it is not associated with the vanishing of the effective massive term. Incoherent processes are fundamental to describe such physics.