Topological Protection from Random Rashba Spin-Orbit Backscattering:   Ballistic Transport in a Helical Luttinger Liquid
  The combination of Rashba spin-orbit coupling and potential disorder induces a random current operator for the edge states of a 2D topological insulator. We prove that charge transport through such an edge is ballistic at any temperature, with or without Luttinger liquid interactions. The solution exploits a mapping to a spin 1/2 in a time-dependent field that preserves the projection along one randomly undulating component (integrable dynamics). Our result is exact and rules out random Rashba backscattering as a source of temperature-dependent transport, absent integrability-breaking terms. 
Hong-Yi Xie, Heqiu Li, Yang-Zhi Chou, and Matthew S. Foster
cond-mat.mes-hall cond-mat.str-el