  Topological insulators (TIs) represent a new quantum state of matter
characterized by robust gapless states inside the insulating bulk gap. The
metallic edge states of a two-dimensional (2D) TI, known as quantum spin Hall
(QSH) effect, are immune to backscattering and carry fully spin-polarized
dissipationless currents. However, existing 2D TIs realized in HgTe and
InAs/GaSb suffer from small bulk gaps (<10 meV) well below room temperature,
thus limiting their application in electronic and spintronic devices. Here, we
report a new 2D TI comprising a graphene layer sandwiched between two Bi2Se3
slabs that exhibits a large intrinsic bulk band gap of 30 to 50 meV, making it
viable for room-temperature applications. Distinct from previous strategies for
enhancing the intrinsic spin-orbit coupling effect of the graphene lattice, the
present graphene-based TI operates on a new mechanism of strong inversion
between graphene Dirac bands and Bi2Se3 conduction bands. Strain engineering
leads to effective control and substantial enhancement of the bulk gap.
Recently reported synthesis of smooth graphene/Bi2Se3 interfaces demonstrates
feasibility of experimental realization of this new 2D TI structure, which
holds great promise for nanoscale device applications.
