Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA.
Phys Rev Lett. 2011 Dec 16;107(25):256801. doi: 10.1103/PhysRevLett.107.256801. Epub 2011 Dec 14.
We show that gated bilayer graphene hosts a strong topological insulator (TI) phase in the presence of Rashba spin-orbit (SO) coupling. We find that gated bilayer graphene under preserved time-reversal symmetry is a quantum valley Hall insulator for small Rashba SO coupling λ(R), and transitions to a strong TI when λ(R)>√[U(2)+t(⊥)(2)], where U and t(⊥) are, respectively, the interlayer potential and tunneling energy. Different from a conventional quantum spin Hall state, the edge modes of our strong TI phase exhibit both spin and valley filtering, and thus share the properties of both quantum spin Hall and quantum valley Hall insulators. The strong TI phase remains robust in the presence of weak graphene intrinsic SO coupling.
我们表明，在存在拉什巴自旋轨道（SO）耦合的情况下，门控双层石墨烯具有强拓扑绝缘体（TI）相。我们发现，在时间反演对称性保持不变的情况下，小拉什巴 SO 耦合 λ(R)下的门控双层石墨烯是量子谷霍尔绝缘体，当 λ(R)>√[U(2)+t(⊥)(2)]时，它会转变为强 TI，其中 U 和 t(⊥)分别是层间势和隧道能。与传统的量子自旋霍尔态不同，我们的强 TI 相的边缘模式同时具有自旋和谷过滤，因此具有量子自旋霍尔和量子谷霍尔绝缘体的共同特性。在存在弱石墨烯本征 SO 耦合的情况下，强 TI 相仍然稳健。
