Electron Pairs Survive to Room Temperature in High-Temperature Superconductor, Science Study Finds

Physicists in the Netherlands and Germany report that the electron pairs needed for superconductivity can exist at room temperature, which narrows the search for materials that conduct electricity with zero resistance without extreme cooling. The study, published in Science, came from teams at Utrecht University, Leiden University and Munich.

Superconductivity lets a material carry current with no resistance, which could enable levitating trains, ultra-efficient energy storage and better quantum computers. The catch is cold. Many conventional superconductors must be cooled to around minus 260 degrees Celsius with liquid helium, an expensive and energy-intensive process. Superconductivity was discovered in 1911. In the mid-1980s researchers found materials that superconduct at much higher temperatures, though still around minus 173 degrees Celsius.

The theory that explains the conventional, low-temperature kind could not account for those newer materials, and scientists still do not understand how they work. "We don't understand superconductivity at these higher temperatures at all," said Ingmar Swart, one of the research leaders. "And if you don't understand it, you can't systematically search for materials that become superconducting at room temperature, which is ultimately our goal."

The team worked with a copper-oxide compound, Bi2Sr2CaCu2O8+δ, and used atomic-scale microscopy measurements to examine electrons. Their paper, titled "Equivalence of pseudogap and pairing energy in a cuprate high-temperature superconductor," concludes that the energy gap seen above the superconducting transition temperature reflects electron pairing. In other words, the electrons are already pairing up well above the temperature where superconductivity sets in.

Superconductivity needs two ingredients: electrons must form pairs, known as Cooper pairs, and those pairs must move synchronously. Swart used a dance floor analogy. Ten couples on a floor are not enough if each couple dances alone; they must also move in step. In conventional superconductors, pairing and coordination appear together. The new work shows they do not in high-temperature superconductors.

"The 'glue' that holds the pairs together is strong enough to keep them together even at room temperature," Swart said. "This suggests that the second key ingredient, phase coherence, is the bottleneck." Phase coherence is the synchronized motion of the pairs.

"This is really good news," Swart said. "We show that one of the two key conditions for superconductivity can be met at room temperature. If that weren't possible, room-temperature superconductivity would be out of reach altogether."

The result does not mean a room-temperature superconductor exists. It redirects the hunt toward understanding why the pairs fail to lock into step as the material warms, and Swart said his group plans to focus on phase coherence in follow-up research. If researchers can learn what sustains or destroys that coordination, it may point to a route toward superconductivity at much higher temperatures.