Imaging two-dimensional generalized Wigner crystals
Imaging two-dimensional generalized Wigner crystals
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DOI：
10.1038/s41586-021-03874-9
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发表时间：
2021-09-30
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：
Li, Hongyuan;Li, Shaowei;Wang, Feng
维格纳晶体（1）吸引了凝聚态物理学家近90年（2-14）。二维（2D）维格纳晶体的特征首先在高磁场下的2D电子气中观察到（2-4），最近在过渡金属二硫属化物莫尔超晶格中报道（6-9）。然而，在真实的空间中直接观察二维维格纳晶格仍然是一个突出的挑战。传统的扫描隧道显微镜（STM）具有足够的空间分辨率，但会引起可能改变这种脆弱状态的扰动。在这里，我们展示了真实空间成像的二维维格纳晶体WSe 2/WS 2莫尔异质结使用一个专门设计的非侵入性STM光谱技术。这采用保持接近WSe 2/WS 2莫尔超晶格的石墨烯感测层。进入石墨烯层的局部STM隧道电流由WSe 2/WS 2异质结构中的底层维格纳晶体电子晶格调制。在分数电子填充n = 1/3，1/2和2/3，其中n是每个网站的电子数，不同的维格纳晶格配置，直接可视化。n = 1/3和n = 2/3的维格纳晶体分别呈现三角形和蜂窝晶格，以最小化最近邻占据。n = 1/2态自发地打破了原来的C3对称性，形成条纹相。我们的研究为理解WSe 2/WS 2云纹异质结构中的Wigner晶体态奠定了坚实的基础，并为其他系统中的新型关联电子晶格提供了一种普遍适用的成像方法。
The Wigner crystal(1) has fascinated condensed matter physicists for nearly 90 years(2-14). Signatures of two-dimensional (2D) Wigner crystals were first observed in 2D electron gases under high magnetic field(2-4), and recently reported in transition metal dichalcogenide moire superlattices(6-9). Direct observation of the 2D Wigner crystal lattice in real space, however, has remained an outstanding challenge. Conventional scanning tunnelling microscopy (STM) has sufficient spatial resolution but induces perturbations that can potentially alter this fragile state. Here we demonstrate real-space imaging of 2D Wigner crystals in WSe2/WS2 moire heterostructures using a specially designed non-invasive STM spectroscopy technique. This employs a graphene sensing layer held close to the WSe2/WS2 moire superlattice. Local STM tunnel current into the graphene layer is modulated by the underlying Wigner crystal electron lattice in the WSe2/WS2 heterostructure. Different Wigner crystal lattice configurations at fractional electron fillings of n = 1/3, 1/2 and 2/3, where n is the electron number per site, are directly visualized. The n = 1/3 and n = 2/3 Wigner crystals exhibit triangular and honeycomb lattices, respectively, to minimize nearest-neighbour occupations. The n = 1/2 state spontaneously breaks the original C3 symmetry and forms a stripe phase. Our study lays a solid foundation for understanding Wigner crystal states in WSe2/WS2 moire heterostructures and provides an approach that is generally applicable for imaging novel correlated electron lattices in other systems.So far, only indirect evidence of Wigner crystals has been reported, but a specially designed scanning tunnelling microscope is used here to directly image them in a moire heterostructure.