In an ultrathin sheet of four-layer graphene, electrons can behave like a frozen liquid. When cooled strongly and subjected to an electric field, they stop darting around and line up into a regular pattern — a Wigner crystal. It's similar to how water droplets on a frosty morning turn into ice honeycombs.
Some of these crystals have a twist: they spontaneously lose their threefold symmetry. A snowflake suddenly stretches in one direction, so do these crystals, becoming asymmetric. They are called nematic. They emerge in two different regimes: at high field and low electron density, and at intermediate field and high density.
Calculations show that half of the asymmetric crystals are stable, while the other half are ready to rearrange into more complex shapes or even turn into a liquid metal. A stable asymmetric crystal can be spotted in an experiment: its charge is distributed unevenly, and electrical resistance depends on direction. It's like water in a river flowing faster along the bank than across it.
The Wigner crystal was predicted back in 1934, but it was first observed only in 1979—on the surface of liquid helium.