Enhanced transport length of spin-helical Dirac fermions in disordered 3D topological insulators

TL;DR

This study experimentally demonstrates that spin-helical Dirac fermions in disordered 3D topological insulators exhibit a significantly enhanced transport length due to anisotropic scattering, indicating potential for long-range spin transport despite disorder.

Contribution

It provides the first experimental measurement of transport length enhancement in disordered 3D topological insulators, confirming theoretical predictions about anisotropic scattering effects.

Findings

Transport length $l_{tr}$ is strongly enhanced for surface states.

The ratio $l_{tr}/l_{e}$ is approximately 8, indicating long-range scattering.

Long spin-flip lengths could be achieved in disordered nanostructures.

Abstract

The transport length $l_\textrm{tr}$ and the mean free path $l_\textrm{e}$ are experimentally determined for bulk and surface states in a Bi$_2$Se$_3$ nanoribbon by quantum transport and transconductance measurements. We show that the anisotropic scattering of spin-helical Dirac fermions results in a strong enhancement of $l_\textrm{tr}$, which confirms theoretical predictions \cite{Culcer2010}. Despite strong disorder ($l_\textrm{e}\approx30$~nm), our result further points to the long-range nature of the scattering potential, giving a large ratio $l_\textrm{tr}/l_\textrm{e}\approx8$ that is likely limited by a finite bulk/surface coupling. This suggests that the spin-flip length could reach the micron size in disordered 3D topological insulator nanostructures with a reduced bulk doping, even if due to charge compensation.