An unexpected observation is shaking up certainties about superconductivity.
Physicists have succeeded in filming the quantum dance of electrons within a superconductor, and the result caught them off guard: pairs of atoms, which were thought to be independent, interact with each other, like dancers synchronized on a crowded stage. This coordinated behavior, never observed before, challenges a 70-year-old theory.
Superconductivity is a phenomenon where certain materials, cooled to extremely low temperatures, allow electric current to pass through without any resistance. This "magical power" comes from the fact that electrons, usually solitary, pair up – they are called Cooper pairs. The theory explaining this mechanism, known as BCS, won its authors a Nobel Prize in the 1950s. But this theory assumes that each pair acts independently, without influencing its neighbors.
For the first time, researchers have imaged the behavior of electron pairs in a superconductor.
Credit: Lucy Reading-Ikkanda/Simons Foundation To verify this hypothesis, physicists from CNRS and the Flatiron Institute designed an ingenious experiment. They used a gas of lithium atoms cooled to a few billionths of a degree above absolute zero. These atoms behave like electrons, allowing the study of superconductivity in a controlled environment. This system, called a Fermi gas, serves as a miniature laboratory to observe quantum mechanics.
Using a new imaging technique, the team took snapshots of the position of each pair of atoms. The images revealed an unexpected organization: the pairs are not randomly distributed but maintain a regular distance from each other, like dancers avoiding bumping into one another. This repulsion pattern, absent from BCS theory, shows that the pairs do interact with each other. The researchers describe this discovery as a "missing piece" of the puzzle.
To ensure these observations were correct, detailed quantum simulations were performed. The calculations exactly reproduced the experimental results, confirming that the pairs organize with precise spacing. This validation strengthens the idea that BCS theory, while useful, is incomplete and that these interactions must be integrated to better understand superconductivity.
These advances could have a considerable impact on the search for new superconducting materials. Currently, the best "high-temperature" superconductors only work at -196 °C (-321 °F), the temperature of liquid nitrogen. By better understanding the fundamental mechanisms, scientists hope one day to create materials that become superconductors at room temperature. Such an achievement would radically transform power grids, computers, and many other technologies.
Beyond superconductivity, this discovery opens a window into other quantum states of matter. By refining their tools on simple systems like the Fermi gas, researchers will be able to explore more complex systems, where perhaps the next major technological innovations lie hidden.