Light Probes and Melts Electron Crystals

Researchers have directly observed and manipulated the internal vibrations of a Wigner crystal using light. The team, led by You Zhou of the University of Maryland, published their findings in Nature Physics on August 28, 2026, detailing a new optical method to probe and control these fragile electron structures.

Wigner crystals form when electrons, repelling each other due to their negative charge, arrange into ordered, crystal-like patterns at low temperatures and densities. Unlike atomic crystals, these are lattices made purely of electrons. They are valuable for testing theories of quantum interactions and phase transitions. Reliable control methods could inform future quantum and electronic devices.

The study focused on a Wigner crystal within a single atomically thin layer of tungsten diselenide (WSe2). The device was cooled to 5 Kelvin. At this temperature and with a low electron density, the electrons' mutual repulsion organized them into the crystal. The researchers then shone light onto the material and measured the reflection spectrum.

Probing Crystal Vibrations with Light

The incoming light created excitons, which are bound pairs of an electron and a hole. These excitons interacted with the Wigner crystal, locally distorting the electron lattice. This distortion, combined with the exciton, forms what the physicists call a Wigner polaron. The optical signal from this polaron revealed the characteristic vibrations, or phonons, of the electron crystal itself.

You Zhou explained the process. He said the exciton dresses itself with the lattice distortion. In optics, they can see absorption from the exciton plus this distortion. This provided a direct probe into the Wigner crystal's internal dynamics, a feat difficult with conventional methods.

Optical Manipulation and Melting

The team demonstrated two key manipulations. First, they used circularly polarized light to control the spins of the electrons in the crystal. This optical method initialized electron spins in a specific direction without needing an external magnetic field.

Second, they found they could melt the crystal. By increasing the optical power to generate a large population of excitons, they destabilized the Wigner crystal. Their measurements showed the phonon energy decreased, indicating the crystal became softer and more likely to melt. Zhou suggested one possible reason is that the excitons screen the Coulomb interactions between the electrons. This provides a method to nonthermally induce a phase transition, potentially at high speed.

The precise mechanism behind the optical melting process remains unclear. The team's paper states that many different possibilities exist. Their work, however, establishes a new approach. It allows for the direct probing of Wigner crystal phonons, spin manipulation, and phase control using only light. This technique could be applied to study Wigner crystals in other two-dimensional materials in the future.