Enhanced Mobility of Spin-Helical Dirac Fermions in Disordered 3D Topological Insulators.

The transport length ltr and the mean free path le are determined for bulk and surface states in a Bi2 Se3 nanoribbon by quantum transport and transconductance measurements. We show that the anisotropic scattering of spin-helical Dirac fermions results in a strong enhancement of ltr (≈ 200 nm) and of the related mobility μtr (≈ 4000 cm2 V-1 s-1 ), which confirms theoretical predictions.1 Despite strong disorder, the long-range nature of the scattering potential gives a large ratio ltr /le ≈ 8, likely limited by bulk/surface coupling. This suggests that the spin-flip length lsf ≈ ltr could reach the micron size in materials with a reduced bulk doping and paves the way for building functionalized spintronic and ballistic electronic devices out of disordered 3D topological insulators.