Electrons usually move more freely at higher temperatures. But they have now been observed to ‘freeze’ as the temperature rises, in a system consisting of two stacked, but slightly misaligned, graphene sheets. In a paper published today in Nature, Brown University Assistant Professor of Physics Jia Leo Li and his colleagues find evidence of a Pomeranchuk-type mechanism in which the liquid ground state freezes upon increasing the temperature in twisted bilayer graphene and related systems.