Fig. 1: STM measurement for Wigner crystal states in a dual gated WSe2/WS2 moir supralattice. Credit: DOI: 10.1038/s41586-021-03874-9
Researchers from the University of California at Berkeley and Lawrence Berkeley National Laboratory have developed a non-invasive method to directly image Wigner crystals. The group published their research in Nature. They describe their method and discuss how it can be used to improve research on Wigner crystal states. Columbia University's Carmen Rubio-Verd has published a News & Views article outlining the nature and work of the Wigner crystals team.
Wigner crystals form when electrons are not evenly distributed in 2D materials. Although they have been seen in liquid helium and 2D semiconductors, they are notoriously difficult or impossible to image. Researchers have created a method to see Wigner crystals in a new way that doesn't disturb them. This allows for better imaging.
Researchers placed a thin layer of tungsten dioxide on top of a thin layer of tungsten deelenide to create a tiny heterostructure. Both are transition-metal dihalcogenides and were only 1 nanometer thick in this case. The electrons were then added to both layers. These 2D structures formed naturally by the team, although the spacing between electrons in one layer was slightly smaller. A moir pattern was created by the mismatch between the electron patterns. This was also a Wigner-crystal. To protect the crystal structure below, researchers added graphene to their heterostructure. They then used a scanning tunnelling microscope to take images of the crystals. To protect the heterostructure, the team later added a layer hexagonal boron Nitride, which allowed for better probing using the microscope.
Researchers also attempted to add and remove electrons from the structure before adding protective barriers. They found that the crystal structures formed into shapes such as triangles and hexagons. Rubio-Verd believes the new technique may lead to new ways to image tiny fragile structures.
Continue reading Researchers trap electrons to make elusive crystals
More information: Hongyuan Li and al., Imaging two-dimensional generalized Wigner s crystals, Nature (2021). Hongyuan Li et al, Imaging two-dimensional generalized Wigner crystals,(2021). DOI: 10.1038/s41586-021-03874-9 Carmen Rubio-Verd, Electron crystals come under the microscope, Nature (2021). DOI: 10.1038/d41586-021-02573-9 Journal information: Nature
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