Topological valley transport at bilayer graphene domain walls
Topological valley transport at bilayer graphene domain walls
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DOI：
10.1038/nature14364
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发表时间：
2015-04-30
期刊：
影响因子：
64.8
通讯作者：
Wang, Feng
中科院分区：
文献类型：
--
作者：
Ju, Long;Shi, Zhiwen;Wang, Feng
电子谷，一个类似于自旋的自由度，可以导致双层石墨烯中的新拓扑相。通过外电场可以在双层石墨烯中诱导可调带隙，并且这种带隙的双层石墨烯被预测为受无谷混合对称性保护的拓扑绝缘相，其特征在于量子谷霍尔效应和手性边缘态。然而，这种手性边缘状态的观察是具有挑战性的，因为谷间散射是由真实的双层石墨烯边缘处的原子尺度缺陷引起的”。最近的理论工作表明，AB和BA堆叠的双层石墨烯之间的畴壁可以支持量子谷霍尔绝缘体的受保护的手征边缘态。在这里，我们报告的实验观察弹道（即没有散射的电子）在双层石墨烯域壁的导电通道。我们采用近场红外纳米尺度显微镜（nanoscopy）对器件衬底上的双层石墨烯层堆叠畴壁进行原位成像，并且我们基于畴壁制造双栅场效应晶体管。与在垂直电场下显示出间隙绝缘行为的单畴双层石墨烯不同，双层石墨烯畴壁具有一维谷极化导电通道，在4开尔文下具有约400纳米的弹道长度。这种拓扑保护的一维手性状态在双层石墨烯畴壁开辟了探索石墨烯中独特的拓扑相和谷物理的机会。
Electron valley, a degree of freedom that is analogous to spin, can lead to novel topological phases in bilayer graphene. A tunable bandgap can be induced in bilayer graphene by an external electric field', and such gapped bilayer graphene is predicted to be a topological insulating phase protected by no-valley mixing symmetry, featuring quantum valley Hall effects and chiral edge states'. Observation of such chiral edge states, however, is challenging because inter-valley scattering is induced by atomic-scale defects at real bilayer graphene edges". Recent theoretical work"' has shown that domain walls between AB- and BA-stacked bilayer graphene can support protected chiral edge states of quantum valley Hall insulators. Here we report an experimental observation of ballistic (that is, with no scattering of electrons) conducting channels at bilayer graphene domain walls. We employ near-field infrared nanometre-scale microscopy (nanoscopy)'" to image in situ bilayer graphene layer-stacking domain walls on device substrates, and we fabricate dual-gated field effect transistors based on the domain walls. Unlike single-domain bilayer graphene, which shows gapped insulating behaviour under a vertical electrical field, bilayer graphene domain walls feature one-dimensional valley-polarized conducting channels with a ballistic length of about 400 nanometres at 4 kelvin. Such topologically protected one-dimensional chiral states at bilayer graphene domain walls open up opportunities for exploring unique topological phases and valley physics in graphene.