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The mystery of quantum phenomena inside materials, such as superconductivity, where current flows without energy loss, lies in when electrons move together and when electrons split. KAIST researchers were able to directly “see” the moments when electrons form and dissolve into regular patterns.

KAIST (Chairman Lee Kwang-hyun) announced on January 20 that a research team including Professor Yang Yong-soo, Professor Lee Sung-bin, Professor Yang Hee-jun, and Professor Kim Yong-kwan from the Department of Physics, in an international joint research project with Stanford University, has spatially visualized the formation and disappearance of charge density waves (CDW)* inside quantum materials.

*CDW (Charge Density Wave): A striped or lattice-like pattern formed when electrons line up at regular intervals like a choreographed dance when certain quantum materials are cooled to extremely low temperatures.

Superconductivity is a state in which current flows only through specific materials at extremely low temperatures with 100% efficiency and no energy loss. Negatively charged electrons normally repel each other, but superconducting electrons are known to pair up and move together in an unusual way. This property is already being exploited in technologies such as MRI scanners and maglev trains. These strongly correlated quantum states, formed by tightly entangled charges, also serve as the basis for next-generation quantum technologies, such as quantum computers.

In order to apply ultralow-temperature quantum phenomena such as superconductivity to quantum computing and related technologies, it is essential to precisely control electrons within materials. However, the spatial pattern of charge density waves formed by electrons at cryogenic temperatures remains largely hidden because it is very difficult to directly observe their formation and disappearance.

The research team used a special liquid helium-cooled electron microscope in conjunction with a four-dimensional scanning transmission electron microscope (4D-STEM) to observe changes in the electron patterns in real time.

This research is similar to using a very high-magnification camera to photograph ice crystals growing as water freezes. The difference is that instead of water, the researchers watched the electrons arrange themselves at a low temperature of about -253 degrees Celsius, and instead of a camera they used an electron microscope that can resolve features as tiny as 1/100,000 times the width of a human hair.

The results showed that the electronic pattern does not appear uniformly throughout the material. In some areas, clear stripes were visible, but in adjacent areas such patterns did not appear at all, giving the appearance of a lake that did not freeze at once but was a mixture of ice and liquid water.

The research team further revealed that this phenomenon is closely related to very subtle internal strains within the material. Small pressures or strains that are invisible to the naked eye can disrupt the formation of electronic patterns.

Conversely, in certain regions, the electronic patterns did not immediately disappear and remained even as the temperature increased. This behavior suggests the existence of isolated “islands” of quantum order that are stable even at high temperatures, but this observation is difficult to explain using existing theoretical frameworks.

Another major achievement of this research was the world’s first quantitative determination of the extent to which the electrons that form charge density waves spatially influence each other. This provides a new analytical framework for understanding how electronic order is connected and maintained within quantum materials, rather than simply identifying whether a pattern exists.

Charge density waves and superconductivity are known to sometimes compete and sometimes cooperate. Therefore, the results of this research naturally lead to research on high-temperature superconductors. Understanding the conditions under which electronic patterns remain stable can open new avenues for researchers to design materials that allow superconducting currents to flow more efficiently.

Professor Yong-soo Yang, who led the research, said, “Until now, we had to rely on theory and indirect measurements to study the subtle changes in electronic order and quantum states at ultralow temperatures.With this research, we are now able to ‘see’ these phenomena directly for the first time.”He added, “By revealing the hidden order in quantum materials, this research is an important breakthrough that will accelerate the development of materials for future quantum technologies.”

This study was conducted in collaboration with Seokjo Hon, Jaewhan Oh, and Jemin Park (KAIST) as co-lead authors. The results were published in Physical Review Letters, a leading international journal in physics, on January 6, 2026.

*Paper title: “Spatial correlation of charge density wave orders across transitions in 2H-NbSe₂”

Doi: https://doi.org/10.1103/776d-dnmf

This research was supported by the National Research Foundation of Korea through the Individual Basic Research Program, Basic Laboratory Program, Nanomaterials Technology Development Program, and KAIST Singularity Professor Program.