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Abstract:
Graphene is the first model system of two-dimensional topological
insulator (TI), also known as quantum spin Hall (QSH) insulator. The QSH
effect in graphene, however, has eluded direct experimental detection
because of its extremely small energy gap due to the weak spin-orbit
coupling. Here we predict by ab initio calculations a giant (three
orders of magnitude) proximity induced enhancement of the TI energy gap
in the graphene layer that is sandwiched between thin slabs of Sb2Te3
(or MoTe2). This gap (1.5 meV) is accessible by existing experimental
techniques, and it can be further enhanced by tuning the interlayer
distance via compression. We reveal by a tight-binding study that the
QSH state in graphene is driven by the Kane-Mele interaction in
competition with Kekule deformation and symmetry breaking. The present
work identifies a new family of graphene-based TIs with an observable
and controllable bulk energy gap in the graphene layer, thus opening a
new avenue for direct verification and exploration of the long-sought
QSH effect in graphene. (C) 2015 Elsevier Ltd. All rights reserved.
