For the first time, researchers have directly visualized the quantum behavior that drives superconductivity, a state in which paired electrons allow electricity to flow with zero resistance at very low temperatures.
But what they observed came as a surprise.
In a study published April 15 in Physical Review Letters, the team captured images of individual atoms forming pairs inside a specially prepared gas cooled to nearly absolute zero — the unreachable limit to how cold anything can get. This system, known as a Fermi gas, lets scientists replace electrons with atoms so they can study superconductivity in a highly controlled environment.
Unexpected Quantum “Dance” Between Paired Particles
After the atoms paired up, the researchers saw something unusual. The pairs did not behave independently. Instead, they moved in a coordinated way, with each pair’s position influenced by nearby pairs — a behavior not predicted by the 70-year-old, Nobel-prize-winning theory of superconductivity.
“Our experiment showed that something is qualitatively missing from this theory,” says experimental research lead Tarik Yefsah of the Laboratoire Kastler Brossel at the French National Centre for Scientific Research (CNRS) in Paris. Yefsah and other experimental physicists at CNRS collaborated on the new study with theoretical physicists, including Shiwei Zhang of the Simons Foundation’s Flatiron Institute.
This discovery adds an important piece to the puzzle of how superconductivity works and may help guide efforts to create room-temperature superconductors, a long-sought goal that could dramatically improve energy efficiency in power grids and electronics.
What Superconductivity Is and Why It Matters
Superconductivity typically appears in certain metals when they are cooled to extremely low temperatures — far colder than anything found naturally on Earth. Once these materials drop below a critical temperature, their electrical resistance suddenly vanishes. This happens because electrons form pairs that move together, often compared to dancers moving in sync across a ballroom floor.
This phenomenon was first explained in the 1950s by physicists John Bardeen, Leon Cooper and John Robert Schrieffer.
Limits of the Classic BCS Theory
However, the BCS theory — named after its creators — provides only an approximate description. It cannot fully explain every type of superconductor or capture all aspects of the behavior involved. Scientists have long suspected that the theory leaves out key details, but those gaps have remained unclear.
“BCS theory tells us superconductivity arises because electrons have a tendency to pair,” says Zhang, a senior research scientist and group leader at the Flatiron Institute’s Center for Computational Quantum Physics (CCQ). “But it’s a rough theory, and it doesn’t tell us anything about how the pairs interact.” According to BCS theory, these pairs act independently, meaning their positions should not depend on one another.
New Imaging Method Reveals Interacting Pairs
To investigate this missing piece, experimental physicists at CNRS worked closely with theorists at CCQ to study how these pairs might influence each other.
Using a newly developed imaging technique, the team captured detailed snapshots of the positions of paired atoms. They worked with a gas of lithium atoms cooled to just a few billionths of a degree Celsius above absolute zero. At such extreme temperatures, the atoms behave as fermions, the same category of particles as electrons, making them ideal stand-ins for studying superconductivity.
The images showed that paired atoms were not randomly distributed. Instead, their positions were linked, with each pair maintaining a certain distance from others, similar to couples on a dance floor avoiding collisions. This behavior reveals an additional layer of organization that is not included in the traditional BCS framework.
A New View Inside the Quantum “Ballroom”
“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.”
To verify the findings, Zhang and his former postdoctoral researcher at the CCQ, Yuan-Yao He of the Institute of Modern Physics at Northwest University in China, carried out detailed quantum simulations of the same system. The simulations matched the experimental data and confirmed the newly observed behavior, including the spacing between the paired “dancers.”
Implications for Future Superconductors
These results deepen scientists’ understanding of superconductors and other quantum materials made of fermions. Insights like this are essential for designing materials that can superconduct at higher temperatures.
In the 1980s, researchers discovered a class of materials known as high-temperature superconductors, which operate at temperatures around that of liquid nitrogen — still a chilly minus 196 degrees Celsius (minus 321 degrees Fahrenheit). Even so, scientists still do not fully understand why these materials work at comparatively higher temperatures.
By improving the fundamental understanding of superconductivity, researchers hope to eventually develop materials that function at everyday temperatures, which could transform energy transmission and computing technologies.
“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.”