Electrical modulation of the edge channel transport in topological insulators coupled to ferromagnetic leads

TL;DR

This study explores how electrical gating influences edge channel transport in two-dimensional topological insulators with ferromagnetic contacts, revealing mechanisms to control spin and charge currents for spintronics applications.

Contribution

It demonstrates that gate-induced inter-edge coupling can modulate charge and spin currents in topological insulators with ferromagnetic leads, offering a new method for device control.

Findings

Inter-edge spin-flip coupling enhances or suppresses current depending on lead magnetization.

Spin-conserving coupling reduces current via backscattering.

Gate voltage modulation can control spin and charge flow in TI-based devices.

Abstract

The counterpropagating edge states of a two-dimensional topological insulator (TI) carry electrons of opposite spins. We investigate the transport properties of edge states in a two-dimensional TI which is contacted to ferromagnetic leads. The application of a side-gate voltage induces a constriction or quantum point contact (QPC) which couples the two edge channels. The transport properties of the system is calculated via the Keldysh nonequilibrium Green's function method. We found that inter-edge spin-flip coupling can significantly enhance (suppress) the charge current when the magnetization of the leads are anti-parallel (parallel) to one another. On the other hand, spin-conserving inter-edge coupling generally reduces the current by backscattering regardless of the magnetization configuration. The charge current and the conductance as a function of the bias voltage, also exhibit similar trends with respect to spin-flip coupling strength, for both parallel and anti-parallel configurations. Hence, gate voltage modulation of edge states via a QPC can provide a means of modulating the spin or charge current flow in TI-based spintronics devices.