A topological current divider

TL;DR

This paper investigates a hybrid ferromagnet-topological insulator junction, revealing a topological current divider effect where spin-polarized currents are asymmetrically split, with potential applications in spintronics for measuring current polarization.

Contribution

It introduces a novel topological current divider mechanism based on the interplay between ferromagnetic polarization and helical edge states, demonstrating asymmetric current splitting.

Findings

Spin-polarized current is asymmetrically divided into separate edge channels.

The branch current ratio depends on the polarization of the injected current.

The effect offers a new method to measure current polarization in spintronics.

Abstract

We study the transport properties of a hybrid junction made of a ferromagnetic lead in electrical connection with the helical edge modes of a two-dimensional topological insulator. In this system, the time reversal symmetry, which characterizes the ballistic edge modes of the topological insulator, is explicitly broken inside the ferromagnetic region. This conflict situation generates unusual transport phenomena at the interface which are the manifestation of the interplay between the spin polarization of the injected current and the spin-momentum locking mechanism operating inside the topological insulator. We show that the spin polarized current originated in the ferromagnetic region is asymmetrically divided in spatially separated branch currents sustained by edge channels with different helicity inside the topological insulator. The above findings provide the working principle of a topological current divider in which the relative intensity of the branch currents is determined by the polarization of the incoming current. We discuss the relevance of this effect in spintronics where, for instance, it offers an alternative way to measure the current polarization generated by a ferromagnetic electrode.