To capture the clearest and most direct images of a “Wigner crystal”, a structure made entirely of electrons, researchers used a special kind of microscope and two pieces of graphene unusually free of imperfections
By Karmela Padavic-Callaghan
10 April 2024
This is the first direct look at a bizarre crystal made of only electrons
Yazdani Lab, Princeton University
It is hard to coax electrons to form a crystal, and even harder to measure this structure. But physicists have now managed to directly image a “Wigner crystal” – and their images are the clearest ones yet.
“There have been many, literally hundreds, of papers written on finding evidence for the Wigner crystal sort of indirectly,” says Ali Yazdani at Princeton University. “And we never thought that we would succeed in [directly] imaging it. It was a bit of an accident.”
At room temperature, electrons can flow together in electric currents because their kinetic energy overcomes the force that makes particles with the same electric charge repel each other. At very low temperatures, however, repulsive electric forces win out, and the electrons end up arranging themselves into a uniform grid, or a crystal. Physicist Eugene Wigner predicted this phenomenon in 1934, but researchers only recently started to understand how to create Wigner crystals in the lab.
Advertisement
Read more
The multiverse could be much, much bigger than we ever imagined
Yazdani and his colleagues made their Wigner crystal from electrons inside of two thin sheets of graphene, each only one atom thick. To diminish the electrons’ kinetic energy, they put the graphene inside a fridge that cooled it to only a few hundredths of a degree above absolute zero and immersed it in a strong magnetic field.
Yazdani says that it was crucial that their graphene had very few imperfections where electrons could get stuck. Otherwise, the particles could form a crystal-like state because of the structure of those imperfections, rather than because of the interactions with each other, as Wigner predicted.