Physicists have captured direct visual evidence of paired particles coordinating their movements within a superconducting state, revealing a synchronized behavior published April 15 in Physical Review Letters that challenges the 70-year-old theory of zero-resistance electrical flow.
Researchers from the French National Centre for Scientific Research and the Simons Foundation achieved this observation by utilizing a newly developed imaging technique on a specially prepared Fermi gas. The experimental team cooled a cloud of lithium atoms to just a few billionths of a degree Celsius above absolute zero, approaching the unreachable limit of how cold physical matter can get.
At these extreme temperatures, which are far colder than anything found naturally on Earth, the lithium atoms function as fermions. Because fermions belong to the same category of particles as electrons, the supercooled lithium gas serves as a highly controlled macroscopic proxy for the electrical currents inside superconducting metals.
As the temperature dropped toward the absolute physical limit, the lithium atoms formed distinct pairs, replicating the mechanism that allows electricity to flow without resistance. Superconductivity typically appears in certain metals when they are cooled to extremely low temperatures, at which point their electrical resistance suddenly vanishes.
This zero-resistance state occurs because electrons form pairs that move together, a phenomenon often compared to dancers moving in sync across a ballroom floor. Once the lithium atoms paired up in the experimental gas, the imaging data revealed that they did not distribute themselves randomly.
Instead, the pairs maintained specific spatial distances from one another, indicating that the position of any single pair is directly influenced by the proximity of its neighbors. This coordinated positioning contradicts the established BCS theory of superconductivity, formulated in the 1950s by physicists John Bardeen, Leon Cooper, and John Robert Schrieffer.
The Nobel-prize-winning framework posited that electron pairs operate entirely independently once a material drops below its critical temperature. According to the original BCS theory, these pairs act independently, meaning their positions should not depend on one another in any measurable way.
To verify the physical observations captured in Paris, researchers at the Flatiron Institute’s Center for Computational Quantum Physics and the Institute of Modern Physics at Northwest University in China executed comprehensive quantum simulations. Led by theoretical physicists Shiwei Zhang and Yuan-Yao He, the digital models mirrored the experimental lithium gas data precisely.
The simulations confirmed the existence of the spatial spacing between the interacting particles, validating the secondary layer of quantum organization observed in the laboratory. This verified correlation between the physical imaging and the theoretical modeling solidifies the conclusion that the traditional BCS framework provides an incomplete picture of quantum mechanics.
Tarik Yefsah, experimental research lead at the Laboratoire Kastler Brossel at the French National Centre for Scientific Research, noted that the standard theoretical models treat the phenomenon as a closed system where the internal mechanics remain obscured. “Our experiment showed that something is qualitatively missing from this theory,” Yefsah says.
“The BCS theory gives us a view from outside the ballroom, where we can hear the music and see the dancers come out, but we don’t know what’s going on in the ballroom,” Yefsah says. “Our approach is like taking a wide-angle camera inside the ballroom. Now we can see how the dancers are pairing up and paying attention to one another, so they don’t bump into each other.”
Shiwei Zhang, a senior research scientist and group leader at the Flatiron Institute, explained that while the classic framework identifies the basic mechanism of electron pairing, it fails to account for inter-pair dynamics. “BCS theory tells us superconductivity arises because electrons have a tendency to pair,” Zhang says.
“But it’s a rough theory, and it doesn’t tell us anything about how the pairs interact,” Zhang adds. The discovery of this interacting behavior provides essential context for understanding how superconductivity manifests across different types of materials.
Scientists have long suspected that the BCS theory omitted key details, particularly as it cannot fully explain every type of superconductor or capture all aspects of the behavior involved in high-temperature variants. In the 1980s, researchers identified a class of materials capable of superconducting at temperatures around that of liquid nitrogen, which sits at minus 196 degrees Celsius, or minus 321 degrees Fahrenheit.
Despite decades of study, physicists still lack a complete understanding of the mechanisms that allow these specific materials to operate at comparatively higher temperatures than traditional superconductors. Isolating these complex particle interactions provides a necessary foundational step for engineers attempting to synthesize new quantum materials made of fermions.
Achieving zero electrical resistance at everyday temperatures remains a primary objective for modern physics, carrying direct applications for lossless power grids and advanced computing architectures. By improving the fundamental understanding of how these pairs organize themselves, researchers intend to apply these insights toward the development of room-temperature superconductors.
“By understanding this simple case, we can fine-tune our tools to study more complicated systems,” Zhang says. “And more complicated systems are where we look for new phases of matter, which have driven a lot of technological breakthroughs in the past.”
