Spin Conduction in Anisotropic 3-D Topological Insulators

TL;DR

This paper demonstrates that in anisotropic three-dimensional topological insulators, spin lifetimes can be significantly extended by tuning the Hamiltonian or Fermi energy, enabling persistent spin helices and long-distance spin conduction.

Contribution

It introduces mechanisms to break the usual spin lifetime-scattering time link in anisotropic TIs, allowing for enhanced spin conduction and persistent spin helices.

Findings

Spin lifetime can be greatly increased in anisotropic TIs.

Tuning Hamiltonian or Fermi energy enables persistent spin helices.

Derived spin diffusion equations and reported spin lifetimes.

Abstract

When topological insulators possess rotational symmetry their spin lifetime is tied to the scattering time. We show that in anisotropic TIs this tie can be broken and the spin lifetime can be very large. Two different mechanisms can obtain spin conduction over long distances. The first is tuning the Hamiltonian to conserve a spin operator $\cos \phi \, \sigma_x + \sin \phi \, \sigma_y$, while the second is tuning the Fermi energy to be near a local extremum of the energy dispersion. Both mechanisms can produce persistent spin helices. We report spin lifetimes and spin diffusion equations.