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 Bi2Se3 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. 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.