Quasi-ballistic transport of spin-helical Dirac fermions in 3D topological insulator quantum wires

Despite strong disorder, the transport of surface Dirac fermions remains quasi-ballistic in narrow nanowires of a 3D topological insulator, as evidenced in Bi2Se3 or Bi2Te3 quantum wires [1,2]. We demonstrate that such a unique behavior for a mesoscopic conductor results from the spin helicity of all quasi-1D surface modes, rather than from the topological nature of a single perfectly-transmitted mode. The weak coupling of spin-helical modes can be revealed by the non-universal behavior of conductance fluctuations [3], and the spin and energy-dependence of transmissions is well captured by both analytical and numerical models. Under appropriate conditions, such 3DTI quantum wires could be used not only for ballistic spin transport but also as spin filters.

[1] J. Dufouleur et al., Phys. Rev. Lett. 110, 186806 (2013)
[2] L.A. Jauregui et al., Nat. Nano. 11, 345 (2016)
[3] J. Dufouleur et al., Sci. Rep. 7, 45276 (2017)