  We study the suppression of the conductance quantization in quantum spin Hall
systems by a combined effect of electronic interactions and edge disorder, that
is ubiquitous in exfoliated and CVD grown 2D materials. We show that the
interplay between the electronic localized states due to edge defects and
electron-electron interactions gives rise to local magnetic moments, that break
time-reversal symmetry and the topological protection of the edge states in 2D
topological systems. Our results suggest that edge disorder leads to small
deviations of a perfect quantized conductance in short samples and to a strong
conductance suppression in long ones. Our analysis is based on on the Kane-Mele
model, an unrestricted Hubbard mean field Hamiltonian and on a self-consistent
recursive Green's functions technique to calculate the transport quantities.
