Adatoms in graphene nanoribbons: spintronic properties and the quantum spin Hall phase

Abstract

We study the charge and spin transport in a two terminal graphene nanoribbon (GNR) decorated with random distribution of Gold (Au) adatoms using a Kane–Mele model. The presence of the quantum spin Hall (QSH) phase is found to crucially depend on the strength of the intrinsic spin–orbit term, while the plateau in the longitudinal conductance at a value is not the smoking gun for the QSH phase. Thus the Au adatoms which manage to induce only a small intrinsic spin–orbit coupling cannot guarantee a QSH phase, albeit yielding a plateau in the longitudinal conductance around the zero of the Fermi energy. If other adatoms can induce larger spin–orbit strengths (we call them hypothetical adatoms), they would ensure both the plateau and the QSH phase as is evident from the presence of the conducting edge states. Motivated by these results, the spintronic applications are explored via computing the spin polarized conductance for both Au and hypothetical adatoms. The y-component of the spin polarized conductance renders the dominant contribution owing to the finite width of the GNR in the y-direction and is found to possess strikingly similar features with that of the longitudinal conductance. The other two components, namely x and z are small but finite and hence have relevance in spintronic applications. Moreover, via computing the local current distribution, we show the clear emergence of edge states in the case of hypothetical adatoms, which are conspicuously absent for Au decorated GNRs.