Quantum Crystals Reveal a Mysterious Optical Glow

In a breakthrough that could transform the study of strongly correlated quantum matter, researchers at the University of Basel and the Technical University of Munich have developed a way to observe how electrons move collectively inside a Wigner crystal. By using light to interrogate an atomically thin semiconductor, the team detected optical signatures that reveal not only the existence of this elusive state, but also aspects of its internal quantum dynamics.

A Wigner crystal forms when electrons confined to two dimensions interact so strongly that their mutual repulsion overwhelms their tendency to move independently. Instead of behaving like a fluid of freely roaming particles, the electrons arrange themselves into a regular, lattice-like pattern. The phenomenon was predicted by physicist Eugene Wigner nearly a century ago, but observing it experimentally has remained difficult because the crystal is extremely fragile and can be disrupted by temperature, disorder or other environmental influences.

The new experiment was performed using a single atomic layer of tungsten diselenide, a two-dimensional material with unusual electronic and optical properties. The sample was cooled to only a few degrees above absolute zero, creating conditions in which electron interactions become dominant. At these ultralow temperatures, the electrons can organize into a periodic structure. The researchers then illuminated the material and analyzed the light reflected from its surface, searching for changes that could encode the behavior of the electron lattice.

Their measurements revealed previously inaccessible optical features produced by the interaction between the Wigner crystal and excitons. Excitons are quasiparticles formed when light promotes an electron to a higher-energy state, leaving behind a positively charged vacancy known as a hole. The electron and hole remain bound by electrical attraction and can move through the material as a combined entity. In the experiment, these light-generated excitons interacted with the organized electrons, creating hybrid states known as Wigner crystal polarons.

A polaron generally describes a particle dressed by its interaction with the surrounding environment. In this case, the exciton becomes coupled to the collective electronic structure of the Wigner crystal. That coupling modifies the energy and optical response of the exciton, producing distinct features in the reflected-light spectrum. Because the exciton is sensitive to the local electronic environment, these changes act as an indirect probe of the crystal’s arrangement and motion. Rather than attempting to track individual electrons directly, the researchers used the optical response of the hybrid quasiparticle to obtain information about the many-body state.

“Our measurements show that light can do more than simply detect the presence of this exotic state—it can reveal how the state behaves internally,” says first author Lujun Wang of the University of Basel, who conducted the experiments with Ferdinand Menzel, a PhD student in Professor Tomasz Smoleński’s group. The approach provides access to collective properties that are difficult to measure with conventional techniques, particularly in systems where the electrons are locked into delicate, correlated arrangements.

The strength of the electron-electron interaction plays a central role in shaping the observed optical signatures. When the interaction changes, so does the organization and response of the Wigner crystal, and the exciton spectrum changes with it. This relationship gives researchers a way to investigate how the crystal reacts to external perturbations and how its collective excitations emerge. Such excitations are fundamentally different from the motion of a single electron: they involve coordinated changes across the entire electronic lattice, much like phonons describe collective vibrations in an ordinary crystal.

To explain the experimental results, a theoretical team led by Michael Knap at the Technical University of Munich developed a model describing how excitons couple to the collective modes of the Wigner crystal. The theory connects the measured optical features with the underlying many-body physics, showing how the hybrid Wigner crystal polarons can carry information about both the electrons’ spatial organization and their quantum dynamics. “These signals carry information not only about how the electrons are arranged, but also about their quantum dynamics,” says TUM researcher Fabian Pichler. “This allows us to connect the experimental observations directly to the underlying many-body physics.”

The findings establish atomically thin materials as powerful platforms for investigating quantum states governed by strong interactions. They also suggest that optical spectroscopy could become a versatile tool for studying electronic crystals in a range of two-dimensional systems. By turning light-generated excitations into sensitive probes of collective electron motion, the researchers have opened a new window onto a regime of physics where particles no longer behave independently. The work could ultimately help scientists understand how correlated quantum states form, evolve and respond—knowledge that may be important for future technologies based on quantum materials.

Web References: https://doi.org/10.1038/s41567-026-03395-0

References: Nature Physics, DOI: 10.1038/s41567-026-03395-0; article publication date: 11 August 2026.

Keywords

Wigner crystal, quantum materials, tungsten diselenide, excitons, polarons, two-dimensional materials, strongly correlated electrons, quantum dynamics, optical spectroscopy, many-body physics