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MIT Technology Review
Physics

Room-temperature superconductivity has been achieved for the first time

It was in a tiny sample under extremely high pressure, so don’t start dismantling the world’s energy infrastructure quite yet.

Equipment used to create a room-temperature superconductor, including a diamond anvil cell (blue box) and laser arrays, is pictured in the University of Rochester lab of  Ranga Dias.Equipment used to create a room-temperature superconductor, including a diamond anvil cell (blue box) and laser arrays, is pictured in the University of Rochester lab of  Ranga Dias.
Equipment used to create a room-temperature superconductor, including a diamond anvil cell (blue box) and laser arrays, is pictured in the University of Rochester lab of Ranga Dias.Adam Fenster

Room-temperature superconductors—materials that conduct electricity with zero resistance without needing special cooling—are the sort of technological miracle that would upend daily life. They could revolutionize the electric grid and enable levitating trains, among many other potential applications. But until now, superconductors have had to be cooled to extremely low temperatures, which has restricted them to use as a niche technology (albeit an important one). For decades it seemed that room-temperature superconductivity might be forever out of reach, but in the last five years a few research groups around the world have been engaged in a race to attain it in the lab.

One of them just won.

In a paper published today in Nature, researchers report achieving room-temperature superconductivity in a compound containing hydrogen, sulfur, and carbon at temperatures as high as 58 °F (13.3 °C, or 287.7 K). The previous highest temperature had been 260 K, or 8 °F, achieved by a rival group at George Washington University and the Carnegie Institution in Washington, DC, in 2018. (Another group at the Max Planck Institute for Chemistry in Mainz, Germany, achieved 250 K, or -9.7 °F, at around this same time.) Like the previous records, the new record was attained under extremely high pressures—roughly two and a half million times greater than that of the air we breathe.

“It’s a landmark,” says José Flores-Livas, a computational physicist at the Sapienza University of Rome, who creates models that explain high-temperature superconductivity and was not directly involved in the work. “In a couple of years,” he says, “we went from 200 [K] to 250 and now 290. I’m pretty sure we will reach 300.”

Electric currents are flowing electric charges, most commonly made up of electrons. Conductors like copper wires have lots of loosely bound electrons. When an electric field is applied, those electrons flow relatively freely. But even good conductors like copper have resistance: they heat up when carrying electricity.

Superconductivity—in which electrons flow through a material without resistance—sounds impossible at first blush. It’s as though one could drive at high speed through a congested city center, never hitting a traffic light. But in 1911, Dutch physicist Heike Kamerlingh Onnes found that mercury becomes a superconductor when cooled to a few degrees above absolute zero (about -460 °F, or -273 °C). He soon observed the phenomenon in other metals like tin and lead.

For many decades afterwards, superconductivity was created only at extremely low temperatures. Then, in late 1986 and early 1987, a group of researchers at IBM’s Zurich laboratory found that certain ceramic oxides can be superconductors at temperatures as high as 92 K—crucially, over the boiling temperature of liquid nitrogen, which is 77 K. This transformed the study of superconductivity, and its applications in things like hospital MRIs, because liquid nitrogen is cheap and easy to handle. (Liquid helium, though colder, is much more finicky and expensive.) The huge leap in the 1980s led to feverish speculation that room-temperature superconductivity might be possible. But that dream had proved elusive until the research being reported today.

Under pressure

One way that superconductors work is when the electrons flowing through them are “coupled” to phonons—vibrations in the lattice of atoms the material is made out of. The fact that the two are in sync, theorists believe, allows electrons to flow without resistance. Low temperatures can create the circumstances for such pairs to form in a wide variety of materials. In 1968, Neil Ashcroft, of Cornell University, posited that under high pressures, hydrogen would also be a superconductor. By forcing atoms to pack closely together, high pressures change the way electrons behave and, in some circumstances, enable electron-phonon pairs to form.

Scientists have for decades sought to understand just what those circumstances are, and to figure out what other elements might be mixed in with hydrogen to achieve superconductivity at progressively higher temperatures and lower pressures.

In the work reported in today’s paper, researchers from the University of Rochester and colleagues first mixed carbon and sulfur in a one-to-one ratio, milled the mixture down to tiny balls, and then squeezed those balls between two diamonds while injecting hydrogen gas. A laser was shined at the compound for several hours to break down bonds between the sulfur atoms, thus changing the chemistry of the system and the behavior of electrons in the sample. The resulting crystal is not stable at low pressures—but it is superconducting. It is also very small—under the high pressures at which it superconducts, it is about 30 millionths of a meter in diameter.

The exact details of why this compound works are not fully understood—the researchers aren’t even sure exactly what compound they made. But they are developing new tools to figure out what it is and are optimistic that once they are able to do so, they will be able to tweak the composition so that the compound might remain superconducting even at lower pressures.

Getting down to 100 gigapascal—about half of the pressures used in today’s Nature paper—would make it possible to begin industrializing “super tiny sensors with very high resolution,” Flores-Livas speculates. Precise magnetic sensors are used in mineral prospecting and also to detect the firing of neurons in the human brain, as well as in fabricating new materials for data storage. A low-cost, precise magnetic sensor is the type of technology that doesn’t sound sexy on its own but makes many others possible.

And if these materials can be scaled up from tiny pressurized crystals into larger sizes that work not only at room temperature but also at ambient pressure, that would be the beginning of an even more profound technological shift. Ralph Scheicher, a computational modeler at Uppsala University in Sweden, says that he would not be surprised if this happened “within the next decade.”

Resistance is futile

The ways in which electricity is generated, transmitted, and distributed would be fundamentally transformed by cheap and effective room-temperature superconductors bigger than a few millionths of a meter. About 5% of the electricity generated in the United States is lost in transmission and distribution, according to the Energy Information Administration. Eliminating this loss would, for starters, save billions of dollars and have a significant climate impact. But room-temperature superconductors wouldn’t just change the system we have—they’d enable a whole new system. Transformers, which are crucial to the electric grid, could be made smaller, cheaper, and more efficient. So too could electric motors and generators. Superconducting energy storage is currently used to smooth out short-term fluctuations in the electric grid, but it still remains relatively niche because it takes a lot of energy to keep superconductors cold. Room-temperature superconductors, especially if they could be engineered to withstand strong magnetic fields, might serve as very efficient way to store larger amounts of energy for longer periods of time, making renewable but intermittent energy sources like wind turbines or solar cells more effective.

And because flowing electricity creates magnetic fields, superconductors can also be used to create powerful magnets for applications as diverse as MRI machines and levitating trains. Superconductors are of great potential importance in the nascent field of quantum computing, too. Superconducting qubits are already the basis of some of the world’s most powerful quantum computers. Being able to make such qubits without having to cool them down would not only make quantum computers simpler, smaller, and cheaper, but could lead to more rapid progress in creating systems of many qubits, depending on the exact properties of the superconductors that are created.

All these applications are in principle attainable with superconductors that need to be cooled to low temperatures in order to work. But if you have to cool them so radically, you lose many—in some cases all—of the benefits you get from the lack of electrical resistance. It also makes them more complicated, expensive, and prone to failure.

It remains to be seen whether scientists can devise stable compounds that are superconducting not only at ambient temperature, but also at ambient pressure. But the researchers are optimistic. They conclude their paper with this tantalizing claim: “A robust room-temperature superconducting material that will transform the energy economy, quantum information processing and sensing may be achievable.”