Update (November 9, 2023): This week the journal Nature retracted the lutetium superconductivity study on request of some of the co-authors and other physicists who questioned the electrical resistance data. The story below, which focused on the challenge of achieving room-temperature superconductivity and the controversy around the lutetium claims, has been updated to reflect the retraction.
In the future, wires might cross underneath oceans to effortlessly deliver electricity from one continent to another. Those cables would carry currents from giant wind turbines or power the magnets of levitating high-speed trains.
All these technologies rely on a long-sought wonder of the physics world: superconductivity, a heightened physical property that lets metal carry an electric current without losing any juice.
But superconductivity has only functioned at freezing temperatures that are far too cold for most devices. To make it more useful, scientists have to recreate the same conditions at regular temperatures. And even though physicists have known about superconductivity since 1911, a room-temperature superconductor still evades them, like a mirage in the desert.
What is a superconductor?
All metals have a point called the “critical temperature.” Cool the metal below that temperature, and electrical resistivity all but vanishes, making it extra easy to move charged atoms through. To put it another way, an electric current running through a closed loop of superconducting wire could circulate forever.
Today, anywhere from 8 to 15 percent of mains electricity is lost between the generator and the consumer because the electrical resistivity in standard wires naturally wicks some of it away as heat. Superconducting wires could eliminate all of that waste.
There’s another upside, too. When electricity flows through a coiled wire, it produces a magnetic field; superconducting wires intensify that magnetism. Already, superconducting magnets power MRI machines, help particle accelerators guide their quarry around a loop, shape plasma in fusion reactors, and push maglev trains like Japan’s under-construction Chūō Shinkansen.
Turning up the temperature
While superconductivity is a wondrous ability, physics nerfs it with the cold caveat. Most known materials’ critical temperatures are barely above absolute zero (-459 degrees Fahrenheit). Aluminum, for instance, comes in at -457 degrees Fahrenheit; mercury at -452 degrees Fahrenheit; and the ductile metal niobium at a balmy -443 degrees Fahrenheit. Chilling anything to temperatures that frigid is tedious and impractical.
Scientists made it happen—in a limited capacity—by testing it with exotic materials like cuprates, a type of ceramic that contains copper and oxygen. In 1986, two IBM researchers found a cuprate that superconducted at -396 degrees Fahrenheit, a breakthrough that won them the Nobel Prize in Physics. Soon enough, others in the field pushed cuprate superconductors past -321 degrees Fahrenheit, the boiling point of liquid nitrogen—a far more accessible coolant than the liquid hydrogen or helium they’d otherwise need.
“That was a very exciting time,” says Richard Greene, a physicist at the University of Maryland. “People were thinking, ‘Well, we might be able to get up to room temperature.’”
Now, more than 30 years later, the search for a room-temperature superconductor continues. Equipped with algorithms that can predict what a material’s properties will look like, many researchers feel that they’re closer than ever. But some of their ideas have been controversial.
The replication dilemma
One way the field is making strides is by turning the attention away from cuprates to hydrates, or materials with negatively charged hydrogen atoms. In 2015, researchers in Mainz, Germany, set a new record with a sulfur hydride that superconducted at -94 degrees Fahrenheit. Some of them then quickly broke their own record with a hydride of the rare-earth element lanthanum, pushing the mercury up to around -9 degrees Fahrenheit—about the temperature of a home freezer.
But again, there’s a catch. Critical temperatures shift when the surrounding pressure changes, and hydride superconductors, it seems, require rather inhuman pressures. The lanthanum hydride only achieved superconductivity at pressures above 150 gigapascals—roughly equivalent to conditions in the Earth’s core, and far too high for any practical purpose in the surface world.
So imagine the surprise when mechanical engineers at the University of Rochester in upstate New York presented a hydride made from another rare-earth element, lutetium. According to their results, which have since been retracted, the lutetium hydride superconducts at around 70 degrees Fahrenheit and 1 gigapascal. That’s still 10,000 times Earth’s air pressure at sea level, but low enough to be used for industrial tools.
“It is not a high pressure,” says Eva Zurek, a theoretical chemist at the University at Buffalo. “If it can be replicated, [this method] could be very significant.”
Scientists, however, have seen this kind of an attempt before. In 2020, the same research group claimed they’d found room-temperature superconductivity in a hydride of carbon and sulfur. After the initial fanfare, many of their peers pointed out that they’d mishandled their data and that their work couldn’t be replicated. Eventually, the University of Rochester engineers caved and retracted that paper as well.
Now, they’re facing the same questions with their lutetium superconductor. “It’s really got to be verified,” says Greene. The early signs are inauspicious: A team from Nanjing University in China recently tried to replicate the experiment, without success.
“Many groups should be able to reproduce this work,” Greene adds. “I think we’ll know very quickly whether this is correct or not.”
But if the new hydride does mark the first room-temperature superconductor—what next? Will engineers start stringing power lines across the planet tomorrow? Not quite. First, they have to understand how this new material behaves under different temperatures and other conditions, and what it looks like at smaller scales.
“We don’t know what the structure is yet. In my opinion, it’s going to be quite different from a high-pressure hydride,” says Zurek.
If the superconductor is viable, engineers will have to learn how to make it for everyday uses. But if they succeed, the result could be a gift for world-changing technologies.