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

摘要

The counterpropagating edge states of a two-dimensional topological insulator(TI) carry electrons of opposite spins. We investigate the transport propertiesof edge states in a two-dimensional TI which is contacted to ferromagneticleads. The application of a side-gate voltage induces a constriction or quantumpoint contact (QPC) which couples the two edge channels. The transportproperties of the system is calculated via the Keldysh nonequilibrium Green'sfunction method. We found that inter-edge spin-flip coupling can significantlyenhance (suppress) the charge current when the magnetization of the leads areanti-parallel (parallel) to one another. On the other hand, spin-conservinginter-edge coupling generally reduces the current by backscattering regardlessof the magnetization configuration. The charge current and the conductance as afunction of the bias voltage, also exhibit similar trends with respect tospin-flip coupling strength, for both parallel and anti-parallelconfigurations. Hence, gate voltage modulation of edge states via a QPC canprovide a means of modulating the spin or charge current flow in TI-basedspintronics devices.