Electron movement spotted in fragile quantum state using light by scientists

Researchers at the University of Basel, Switzerland and Technical University of Munich, have developed a new approach that reveals the motion of electrons in the Wigner crystal, one of the most elusive states of matter. The team was able to access properties of the crystal in its fragile quantum state using light. First predicted nearly a century ago, the Wigner crystal is a solid phase of electrons that forms a organized crystal-like lattice structure at low densities. When moving in an inert, neutralizing background, a gas of electrons tend to crystallize at low densities as their potential energy is more dominant than their kinetic energy. Depending on the number of dimensions, the electrons are spread in, they can either form a crystal lattice in 3D, a triangular lattice when in two dimensions or an evenly space latticed when in a single dimension, as the electron cloud looks to minimize its potential energy. Physicist Eugene Winger predicted this in 1934 and has fascinated scientists since because it does not arise from an internal structure from the host material. While these crystals have been observed extensively, little was known about their internal behavior, their movements, interactions or responses to external disturbances. So, a team of researchers led by Tomasz Smoleński, assistant professor at the University of Basel, probed the crystal using light. The research team cooled a single layer of tungsten diselenide to temperatures just above absolute zero and illuminated it using light. “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,” explained Lujun Wang, who carried out the experiments at the University of Basel. Their work showed that the optical signatures were influenced by the strength of the interactions among the electrons, which is useful in exploring other systems which have multiple interacting particles. To make sense of their find, the researchers also needed a strong theory of what was happening inside the Wigner crystal. So, the team collaborated with Michael Knap, a professor of collective quantum dynamics at the Technical University of Munich (TUM) to understand what was happening. New window for other materials Knap and his team came up with the theory that the incident light generated excitons which interacted with the orderly arrangement of electrons in the Wigner crystal and resulted in the formation of hybrid quasiparticles called polarons. These polarons served as optical probes for the crystal and its collective dynamics. “What is particularly exciting is that these signals carry information not only about how the electrons are arranged, but also about their quantum dynamics,” explained Fabian Pichler, a PhD student at TUM and member of Knap’s research team. “This allows us to connect the experimental observations directly to the underlying many-body physics.” The study demonstrates that atomically thin materials are promising platform for viewing collective motion of electrons in ordered quantum states. This opens up possibilities of investigating other materials and understanding its internal dynamics even if it may have strongly correlated matter. The research findings were published in the journal Nature Physics. Recommended ArticlesGet the latest in engineering, tech, space & science - delivered daily to your inbox.Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.