Extreme cold is usually required to achieve superconductivity, as demonstrated in this photo from Dias's lab, in which a magnet floats above a superconductor cooled with liquid nitrogen. Image: University of Rochester photo/J. Adam Fenster.
Extreme cold is usually required to achieve superconductivity, as demonstrated in this photo from Dias's lab, in which a magnet floats above a superconductor cooled with liquid nitrogen. Image: University of Rochester photo/J. Adam Fenster.

By compressing simple molecular solids with hydrogen at extremely high pressures, a team led by researchers at the University of Rochester has, for the first time, created a material that is superconducting at room temperature. Reported in a paper in Nature, this work was conducted in the lab of Ranga Dias, an assistant professor of physics and mechanical engineering at the University of Rochester.

According to Dias, developing materials that are superconducting – meaning they lack electrical resistance and expel magnetic fields – at room temperature is the "holy grail" of condensed matter physics. Sought for more than a century, such materials "can definitely change the world as we know it", he says.

To set this new record, Dias and his research team combined hydrogen with carbon and sulfur to photochemically synthesize simple organic-derived carbonaceous sulfur hydride in a diamond anvil cell, a research device used to examine miniscule amounts of materials under extraordinarily high pressure. The carbonaceous sulfur hydride exhibited superconductivity at about 58°F and a pressure of about 39 million psi. This is the first time that a superconducting material has been observed at room temperatures.

"Because of the limits of low temperature, materials with such extraordinary properties have not quite transformed the world in the way that many might have imagined. However, our discovery will break down these barriers and open the door to many potential applications," says Dias.

These applications could include: power grids that transmit electricity without the loss of up to 200 million megawatt hours (MWh) of energy, which currently occurs due to resistance in the wires; a new way to propel levitated trains and other forms of transportation; medical imaging and scanning techniques such as MRI and magnetocardiography; and faster, more efficient electronics for digital logic and memory device technology.

"We live in a semiconductor society, and with this kind of technology, you can take society into a superconducting society where you'll never need things like batteries again," says Ashkan Salamat of the University of Nevada Las Vegas, a co-author of the paper.

The amount of superconducting material created by the diamond anvil cells is measured in picoliters – about the size of a single inkjet particle. The next challenge, Dias says, is finding ways to create the room-temperature superconducting material at lower pressures, so it will be economical to produce in greater volumes. In comparison to the millions of pounds of pressure created in diamond anvil cells, the atmospheric pressure of Earth at sea level is about 15 psi.

First discovered in 1911, superconductivity gives materials two key properties. Their electrical resistance vanishes, while any semblance of a magnetic field is expelled, due to a phenomenon called the Meissner effect. Magnetic field lines have to pass around the superconducting material, making it possible to levitate such materials, something that could be used for frictionless high-speed trains, known as maglev trains.

Powerful superconducting electromagnets are already critical components of maglav trains, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) machines, particle accelerators and other advanced technologies, including early quantum supercomputers.

But the superconducting materials used in these devices usually work only at extremely low temperatures – lower than any natural temperatures on Earth. This restriction makes them costly to maintain – and too costly to extend to other potential applications. "The cost to keep these materials at cryogenic temperatures is so high you can't really get the full benefit of them," Dias says.

Previously, the highest temperature for a superconducting material was achieved last year by the lab of Mikhail Eremets at the Max Planck Institute for Chemistry in Mainz, Germany, and the Russell Hemley group at the University of Illinois at Chicago. That team reported superconductivity at between -10°F and 8°F using lanthanum superhydride.

Researchers have also explored copper oxides and iron-based chemicals as potential candidates for high-temperature superconductors in recent years. However, hydrogen – the most abundant element in the universe – also offers a promising building block.

"To have a high-temperature superconductor, you want stronger bonds and light elements. Those are the two very basic criteria," Dias says. "Hydrogen is the lightest material, and the hydrogen bond is one of the strongest.

"Solid metallic hydrogen is theorized to have high Debye temperature and strong electron-phonon coupling that is necessary for room temperature superconductivity."

However, extraordinarily high pressures are needed just to get pure hydrogen into a metallic state, which was first achieved in a lab in 2017 by Isaac Silvera at Harvard University and Dias, then a postdoc in Silvera's lab. And so, Dias's lab at Rochester has pursued a 'paradigm shift' in its approach, by using hydrogen-rich materials that mimic the elusive superconducting phase of pure hydrogen but can be metalized at much lower pressures.

First the lab combined yttrium and hydrogen. The resulting yttrium superhydride exhibited superconductivity at what was then a record high temperature of about 12°F and a pressure of about 26 million pounds per square inch. Next the lab explored covalent hydrogen-rich organic-derived materials, which resulted in the carbonaceous sulfur hydride.

"This presence of carbon is of tantamount importance here," the researchers report. Further "compositional tuning" of this combination of elements may be the key to achieving superconductivity at even higher temperatures, they add.

This story is adapted from material from the University of Rochester, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.