Effects of Defects and Dephasing on Charge and Spin Currents in Two-Dimensional Topological Insulators

TL;DR

This paper explores how defects and dephasing influence charge and spin transport in two-dimensional topological insulators, revealing robustness of spin-polarized currents and potential for novel quantum effects.

Contribution

It demonstrates the effects of various defects on electronic structure and transport in 2D TIs, including the robustness of spin-polarized currents against dephasing and Rashba interactions.

Findings

Defects alter local electronic structure and transport in TIs.

Spin-polarized currents remain stable despite dephasing and Rashba effects.

Sign of spin currents changes under symmetry operations.

Abstract

Using the non-equilibrium Keldysh Green's function formalism, we investigate the effect of defects on the electronic structure and transport properties of two-dimensional topological insulators (TI). We demonstrate how the spatial flow of charge changes between the topologically protected edge and bulk states and show that elastically and inelastically scattering defects that preserve the time reversal symmetry of the TI lead to qualitatively different effects on the TI's local electronic structure and its transport properties. Moreover, we show that the recently predicted ability to create highly spin-polarized currents by breaking the time-reversal symmetry of the TI via magnetic defects [Phys. Rev. B 93, 081401 (2016)] is robust against the inclusion of a Rashba spin-orbit interaction and the effects of dephasing, and remains unaffected by changes over a wide range of the TI's parameters. We discuss how the sign of the induced spin currents changes under symmetry operations, such as reversal of bias and gate voltages, or spatial reflections. Finally, we show that the insight into the interplay between topology and symmetry of the magnetic defects can be employed for the creation of novel quantum phenomena, such as highly localized magnetic fields inside the TI.