A layer of electrons trapped between two semiconductor plates lines up into a neat lattice at low temperatures, like beads on a string stretched between your fingers. As the temperature rises, order collapses: the crystal melts. But exactly how it melts has long been a puzzle.
Researchers took an ultra-clean gallium arsenide crystal with a quantum well — a thin layer where electrons can move only in a plane. In a strong magnetic field, the electrons gathered into "bubbles"—groups that arranged into a lattice. They ran a current through the sample and watched at what temperature the order vanished. It turned out that melting begins with the appearance of defect pairs — tiny vortices in the lattice, like two swirling funnels in water. These pairs tear apart, and the crystal falls apart.
Calculations including these vortices gave a melting temperature that matched the experiment for different Landau levels — the "steps" of electron energy in a magnetic field. The match is not approximate but quantitative: where theory says "still a crystal here," current flows as through a solid, and where "already a liquid," resistance changes. This means defects truly govern the melting of the electronic crystal.
This approach can be extended to other electronic crystals, such as the Wigner crystal in twisted graphene layers. Understanding how these structures melt will help create more stable electronic devices of the future.
The melting temperature of the electronic crystal in this experiment is fractions of a kelvin — colder than outer space.
In Peter Watts's novel Blindsight, alien intelligence is built on quantum effects, and here a quantum crystal melts by strict rules of defects.