Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China.
Department of Physics, University of Texas at Dallas, Richardson, TX, 75080, USA.
Nat Commun. 2019 Feb 5;10(1):611. doi: 10.1038/s41467-019-08629-9.
Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom in addition to charge and spin. In the absence of inversion symmetry, these systems were predicted to exhibit opposite Hall effects for electrons from different valleys. Such valley Hall effects have been achieved only by extrinsic means, such as substrate coupling, dual gating, and light illuminating. Here we report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS, evidenced by considerable nonlocal resistance that scales cubically with local resistance. Such a hallmark survives even at room temperature with a valley diffusion length at micron scale. By contrast, no valley Hall signal is observed in the centrosymmetric bilayer MoS. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics.
电子在二维蜂窝状晶格中的跃迁除了电荷和自旋外，还具有谷自由度。在没有反转对称的情况下，这些系统被预测会表现出来自不同谷的电子的相反的霍尔效应。这种谷霍尔效应仅通过外在手段实现，例如衬底耦合、双栅极和光照。在这里，我们报告了在非中心对称单层和三层 MoS 中没有任何外在对称破坏的固有谷霍尔输运的首次观察，这一点通过与局部电阻成三次方比例的相当大的非局部电阻来证明。即使在室温下，这种标志也能保持，谷扩散长度可达微米级。相比之下，在中心对称的双层 MoS 中观察不到谷霍尔信号。我们的工作阐明了谷霍尔效应的拓扑起源，并朝着在拓扑谷电子学中纯电控制谷自由度迈出了重要的一步。
