Yonsei University researchers uncover direct evidence of wigner crystals and electronic rotons
Elusive electronic rotons, detected for the first time, reveal the formation of Wigner crystallites in a two-dimensional electron liquid
image: Researchers have uncovered tiny flakes of Wigner crystals—unique structures formed entirely by electrons—by identifying unusual, aperiodic electronic signals. This breakthrough method reveals hidden aspects of electron behavior and paves the way for advancements in understanding complex electronic interactions.
Credit: Keun Su Kim from Yonsei University, Korea
For decades, researchers have explored how electrons behave in quantum materials. Under certain conditions, electrons interact strongly with each other instead of moving independently, leading to exotic quantum states. One such state, first proposed by Nobel laureate Eugene Wigner, is the Wigner crystal—a structured electron arrangement caused by their mutual repulsion. Although widely theorized, experimental proof has been rare.
Researchers at Yonsei University have provided evidence of Wigner crystallization and the associated electronic rotons. In a study published in volume 634 of the journal Nature, on October 16, 2024, Prof. Keun Su Kim and his team used angle-resolved photoemission spectroscopy (ARPES) to analyze black phosphorus doped with alkali metals. Their data revealed aperiodic energy variations, a hallmark of electronic rotons. Crucially, as they decreased the dopant density within the material, the roton energy gap shrank to zero. This observation confirmed a transition from a fluid-like quantum state to a structured electron lattice, characteristic of Wigner crystallization.
“Electrons are known to behave like waves, moving freely in solids. However, Wigner proposed that at low densities, strong repulsion between electrons could immobilize them into a crystal-like structure. Here, we identified flakes of such Wigner crystals by detecting anomalously aperiodic signals in ARPES data from alkali metals on black phosphorus,” explains Prof. Kim, lead researcher of the study.
The researchers found that the energy patterns of the electrons were irregular, showing a dip at a certain momentum. This irregular pattern, not seen in regular crystalline solids, strongly indicated the presence of electronic rotons. By looking at how the electrons were arranged, using a technique called structure factor analysis, they confirmed that the electrons had a short-range order, which is important for forming these Wigner crystals.
Using structure factor analysis, the researchers found that as the Wigner crystal formed, the electrons became more evenly spaced. This showed that tiny, ordered groups of electrons—like mini-crystals—were forming within the material.
This discovery is a major step in understanding how electrons behave in strongly correlated systems. The Wigner crystal has been proposed as a key to understanding the mechanism of high-temperature superconductivity and superfluidity. “Once we can understand high-temperature superconductivity, it will totally change our real life. Phones and computers will never overheat no matter how long one uses them. There will be no energy loss in electricity transmission, lowering energy costs. Lastly, we will see revolutionary changes in transportation, like magnetic levitation trains becoming more affordable,” says Prof. Kim.
While this study focuses on fundamental physics, its implications extend far beyond. By deepening our understanding of quantum materials, this work moves us closer to one day achieving room-temperature superconductors, which could transform energy, electronics, and transportation.
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Reference
DOI: 10.1038/s41586-024-08045-0
About the institute
Yonsei University, located in Seoul, South Korea, is one of the nation’s oldest and most prestigious private research institutions. Founded in 1885, the university is renowned for academic excellence and its strong commitment to international collaborations and partnerships. Yonsei offers diverse programs across the humanities, sciences, engineering, business, and more, serving approximately 30,000 students with a distinguished faculty. Yonsei remains dedicated to fostering creativity and cultural exchange in a rapidly evolving world.
https://www.yonsei.ac.kr/en_sc/
About Prof. Keun Su Kim
Prof. Keun Su Kim is an Underwood Distinguished Professor of Physics and Director of the Center for Bandstructure Engineering at Yonsei University. His research group investigates the electronic structure of quantum materials for use in next-generation semiconductor and quantum technologies. Before joining Yonsei University, he served as an assistant professor of Physics at Pohang University of Science and Technology (POSTECH). He completed his postdoctoral training at Lawrence Berkeley National Lab. In 2010, he received a PhD in Physics from Yonsei University.