If the conditions are right, the electrons in a material organize themselves into a neat honeycomb pattern. Physicists now directly map such Wigner’s crystals as they did Report in the journal “Nature”.
The crystals are named after the Hungarian-born theorist Eugene Wigner, who first introduced them nearly 90 years ago. The study’s co-authors say that researchers had previously prepared Wigner’s crystals and measured their properties, but this is the first time that anyone has actually taken a snapshot of the pattern. Fang Wang, a physicist at the University of California, Berkeley. “If you say you have an electron crystal, show me the crystal,” he says.
To build the structures, Wang’s team built a device with atomically thin layers of two similar semiconductors: tungsten disulfide and tungsten diselenide. The team then used an electric field to adjust the density of freely moving electrons at the interface between the two layers.
In normal materials, electrons spin very rapidly, which are greatly influenced by the repulsion between their negative charges. However, Wigner predicted that this repulsion would dominate their behavior if the electrons moved slowly enough. The electrons would then find arrangements that minimize their total energy, like a honeycomb pattern. Wang and his colleagues slowed them down by cooling the electrons in their device to a few degrees above absolute zero.
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