Perturbative Evidence of Non-Universality in the Quantized Hall   Conductivity of a Disordered Relativistic 2D Electron Gas
  We study a relativistic two-dimensional electron gas in the presence of a uniform external magnetic field and a random static scalar potential. We compute, in first order perturbation theory, the averages of the charge density and of the transverse conductivity for a white-noise potential, and show that, within this treatment, their quantized values are modified by the disorder. 
N. Bralic, C. A. A. de Carvalho, R. M. Cavalcanti and P. Donatis