A domestic research team has made a groundbreaking discovery by finding that electrons within solid materials can exist in an ‘electron crystal’ state, which possesses characteristics of both liquid and solid forms. This discovery, which was only theoretical before, has the potential to provide insights into the mysteries of high-temperature superconductors and superfluid phenomena.
The Ministry of Science and ICT announced that the research results from Professor Geun-Su Kim’s team at Yonsei University’s Department of Physics were published today (17th) in the international journal ‘Nature’.
In solid materials, atoms are arranged in a fixed pattern and cannot move, while electrons can move freely like a gas to create current through flow. Although these electrons exist freely like gas molecules, they can also form a regular, immovable ‘electron crystal’ state due to the repelling force they exert on each other as negatively charged particles.
This theory was initially proposed in the 1930s by Hungarian physicist Eugene Wigner, who received the Nobel Prize in Physics in 1963, as the ‘Wigner Crystal’. If this electron crystal can be realized, it could unlock the secrets of materials like high-temperature superconductors, which can lose resistance above minus 240 degrees Celsius, or superfluid substances, which lose viscosity at extremely low temperatures.
Given that electron interactions influence various properties of materials, such as resistance and viscosity, understanding these interactions to create a crystal could solve many complex issues.
Previously, in 2021, Professor Kim’s team published in Nature their discovery of a liquid-like electron state in a material doped with alkali metals in black phosphorus. Now, they have advanced further to discover for the first time an electron state exhibiting both liquid and solid properties at a specific doping concentration.
In a research briefing held at the Government Complex Sejong by the Ministry of Science and ICT, Professor Kim explained that during the transition of a substance from liquid to solid, not all of it turns solid simultaneously. Instead, solid fragments begin to form sparsely, leading to piece-wise crystallization—a process anticipated theoretically by 21st-century physicists but now confirmed experimentally.
To demonstrate the existence of the electron crystal, the research team employed synchrotron radiation to shine strong light and used angle-resolved photoemission spectroscopy to analyze the information of photoelectrons emitted by the light, accurately measuring the energy and momentum of electrons. They observed unique irregularities in energy and momentum correlations, which differ from the regular patterns seen in gases or solids with perfect crystals, thereby proving the existence of these minuscule electron crystal fragments, which are in the size range of 1–2 nanometers, far smaller than a tenth of a hair’s width.
Professor Kim noted that until now, the academic world has perceived electron arrangements as either regular or irregular, but this new understanding acknowledges a third state. Recognizing the characteristics of these crystals could advance the understanding of the properties of superconductors and superfluids.
He also indicated that instead of just creating new materials to find properties of superconductors, identifying what could raise the superconductive critical temperature opens up possibilities for material design. If the concept of electron crystals could aid in understanding the principles of high-temperature superconductors, it might lead to increases in critical temperature.
Furthermore, Professor Kim mentioned the endeavor to establish a model system for solid-state physics research by focusing on the appearance of electron crystal fragments in high-temperature superconductors alongside the existing systems that dope phosphorus with metals. He highlighted the potential to further explore the fundamental aspects of solid-state physics by doping with alkali earth metals, leading to increased electron injection.
[Image Source: Yonhap News / Provided by Professor Geun-Su Kim at Yonsei University]
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