Levitating trains, ultra-efficient energy storage, and quantum computers: superconductivity could unlock a wealth of possibilities for the future. But there is one major obstacle: most superconductors only work at extremely low temperatures, making practical, large-scale applications difficult and expensive. New research led by scientists from Utrecht, Leiden, and Munich has now shed light on one of the key requirements for achieving superconductivity at room temperature. Their findings, published today in the leading journal Science, bring scientists a step closer to understanding how this might be achieved.
When you turn on a toaster, electricity flows through a metal wire. The wire heats up until it glows red-hot, toasting your bread. This happens because the wire resists the flow of electric current, converting electrical energy into heat.
That is exactly what you want in a toaster. But for most other applications, resistance is undesirable. For example, when you want to charge your phone, resistance causes valuable energy to be lost.
Extremely low temperatures
Superconductivity offers a way around this problem. It is a physical phenomenon in which certain materials conduct electricity without any resistance. The catch? Most superconductors only work at extremely low temperatures. For many materials, this means cooling them to around -260°C using liquid helium. This is an energy-intensive and expensive process.
Early discoveries
Scientists first discovered superconductivity in 1911. In the mid-1980s, they made another breakthrough: the discovery of materials that become superconducting at considerably higher temperatures, although these temperatures were still around -173°C.
There was a problem, however. The theory that explains conventional, low-temperature superconductivity could not account for this new type of superconductivity. And scientists still do not understand how it works.
"We don't understand superconductivity at these higher temperatures at all," says Ingmar Swart [LINK], 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."
New potential route
The new research has helped Swart and his colleagues unravel part of this mystery. Their findings provide new insight into how high-temperature superconductivity works and offer a potential route towards superconductivity at room temperature.
"This is really good news," says Swart. "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."
Dancing pairs
The two key ingredients for superconductivity are the formation of electron pairs, known as Cooper pairs, and the ability of these pairs to move synchronously. Imagine ten couples on a dance floor: it is not enough for each couple to dance together; they must also move in step with one another.
In conventional, low-temperature superconductors, electron pairing and this collective coordination occur together. The new research shows that this is not the case in high-temperature superconductors. In these materials, electrons can already form pairs at temperatures well above the point at which superconductivity sets in.
"The 'glue' that holds the pairs together is strong enough to keep them together even at room temperature," says Swart. "This suggests that the second key ingredient, phase coherence, is the bottleneck."
Swart is referring to the synchronous movement of the pairs, also known as phase coherence. "If we understand phase coherence, it may point to a path toward superconductivity at higher temperatures." Swart plans to focus on this in follow-up research.
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New measuring equipment
The research was made possible by new measuring equipment, developed and built by the researchers themselves. It allowed them to distinguish between electrical current carried by individual electrons and current carried by electron pairs. This gave the team a way to investigate when and how electron pairing occurs in the material.
