Emergent topological properties in interacting one-dimensional systems with spin-orbit coupling

We present analysis of a single-channel interacting quantum wire problem in the presence of spin-orbit interaction. The spin-orbit coupling breaks the spin-rotational symmetry from SU(2) to U(1) and breaks inversion symmetry. The low-energy theory is then a two-band model with a difference of Fermi velocities δv. Using bosonization and a two-loop renormalization group procedure, we show that electron-electron interactions can open a gap in the spin sector of the theory when the interaction strength U is smaller than δv in appropriate units. For repulsive interactions, the resulting strong coupling phase is of the spin-density-wave type. We show that this phase has peculiar emergent topological properties. The gapped spin sector behaves as a topological insulator, with zero-energy edge modes with fractional spin. On the other hand, the charge sector remains critical, meaning the entire system is metallic. However, this bulk electron liquid as a whole exhibits properties commonly associated with the one-dimensional edge states of two-dimensional spin Hall insulators, in particular, the conduction of 2e2/h is robust against nonmagnetic impurities.