Optical measurements can reveal the hidden collective motion and quantum dynamics of electrons inside a Wigner crystal.
In a Wigner crystal, electrons behave in an unusual way. Rather than moving independently, strongly interacting electrons confined to a two-dimensional plane can arrange themselves into a repeating lattice similar to the atoms in an ordinary crystal. Researchers at the University of Basel and the Technical University of Munich have now found a way to use light to examine the collective motion hidden within this fragile quantum state.
Unlike an ordinary crystal, the ordering of a Wigner crystal does not come from the structure of the surrounding material. Instead, it emerges from interactions among the electrons themselves, a property that has made this state of matter an important subject of research for decades.
Wigner crystals have already been observed in several physical systems, but understanding what happens inside them has been far more difficult. In particular, researchers have struggled to measure how their electrons move collectively, interact, and react to external disturbances.
Light exposes hidden electron motion
To investigate those dynamics, experimentalists led by Professor Tomasz Smoleński at the University of Basel studied a single atomic layer of tungsten diselenide cooled to only a few degrees above absolute zero. By shining light onto the material and analyzing what was reflected, they identified previously unseen optical features connected to the collective behavior of electrons in the Wigner crystal. The study was published in Nature Physics.
The signals emerge through interactions between the ordered electrons and excitons, which are excitations produced in the material by light. Together, they form hybrid quasiparticles known as Wigner crystal polarons, which provide a highly sensitive optical probe of the crystal and its collective dynamics.
“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 Dr. Lujun Wang from the University of Basel, who carried out the experiments together with Ferdinand Menzel, a PhD student in Smoleński’s group.
“This gives us a powerful new tool for studying collective excitations of electronic crystals that would otherwise be extremely difficult to access,” adds Smoleński.
The measurements also showed that the strength of interactions among the electrons influences these optical signatures. That connection makes the signals useful for investigating strongly correlated systems, in which interactions among many particles collectively determine the material’s properties.
Optical signals reveal quantum dynamics
To understand the observations, theorists led by Professor Michael Knap at the Technical University of Munich (TUM) developed a theoretical model describing how Wigner crystal polarons form when optically generated excitons couple to the collective motion of electrons in the crystal.
“What is particularly exciting is that these signals carry information not only about how the electrons are arranged, but also about their quantum dynamics,” explains Fabian Pichler, a PhD student at TUM. “This allows us to connect the experimental observations directly to the underlying many-body physics.”
The findings indicate that atomically thin materials can provide a platform for observing the collective movement of electrons within ordered quantum states. By making those internal dynamics accessible through light, the approach could help researchers investigate the fundamental behavior of strongly correlated matter.
Reference: “Spectroscopy of Wigner crystal polarons in an atomically thin semiconductor” by L. Wang, F. Menzel, F. Pichler, P. Knüppel, K. Watanabe, T. Taniguchi, M. Knap and T. Smoleński, 11 August 2026, Nature Physics.
DOI: 10.1038/s41567-026-03395-0
This work was supported by the Swiss National Science Foundation (SNSF) under grant number CRSK-2_237251 as well as by the European Commission through ERC grant OptoQuantTOP (grant number 101219354).
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