Helical edge electron transport in 2D topological insulators

I am interested in mechanisms violating the perfect conductance quantization of the helical edge states:

Inelastic scattering off a generic quantum impurity (no internal degrees of freedom):

http://arxiv.org/abs/1201.0278, http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.156402

Possibility of interference effects in inelastic scattering:

http://arxiv.org/abs/1301.1185, http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.206803

Scattering off charge puddles in a 2D TI (a.k.a narrow-gap semiconductor),

(a) even-charge puddles (no free spins)

http://arxiv.org/abs/1303.1766, http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.216402

(b) any-charge puddles (may carry spins, that enhances substantially the resistance at finite temperatures)

http://arxiv.org/abs/1406.6052

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.115309