Edge states, spin transport and impurity induced local density of states in spin-orbit coupled graphene

TL;DR

This paper investigates edge states, impurity effects, and spin transport in spin-orbit coupled graphene with Zeeman field, revealing robust chiral edge modes, impurity-induced LDOS features, and spin-active junctions that enable electrically controllable spin currents.

Contribution

It demonstrates the existence of chiral edge modes at zigzag interfaces, links LDOS Fourier transforms to spin-orbit strength, and shows spin rotation effects in graphene junctions with potential for spintronic applications.

Findings

Zigzag interfaces host robust chiral edge modes.

LDOS Fourier transform measures spin-orbit coupling strength.

Graphene junctions can generate controllable spin currents.

Abstract

We study graphene which has both spin-orbit coupling (SOC), taken to be of the Kane-Mele form, and a Zeeman field induced due to proximity to a ferromagnetic material. We show that a zigzag interface of graphene having SOC with its pristine counterpart hosts robust chiral edge modes in spite of the gapless nature of the pristine graphene; such modes do not occur for armchair interfaces. Next we study the change in the local density of states (LDOS) due to the presence of an impurity in graphene with SOC and Zeeman field, and demonstrate that the Fourier transform of the LDOS close to the Dirac points can act as a measure of the strength of the spin-orbit coupling; in addition, for a specific distribution of impurity atoms, the LDOS is controlled by a destructive interference effect of graphene electrons which is a direct consequence of their Dirac nature. Finally, we study transport across junctions which separates spin-orbit coupled graphene with Kane-Mele and Rashba terms from pristine graphene both in the presence and absence of a Zeeman field. We demonstrate that such junctions are generally spin active, namely, they can rotate the spin so that an incident electron which is spin polarized along some direction has a finite probability of being transmitted with the opposite spin. This leads to a finite, electrically controllable, spin current in such graphene junctions. We discuss possible experiments which can probe our theoretical predictions.