High-Temperature Superconductor’s High Current Density - IEEE Spectrum

Feb 22, 2025

UPDATE 31 OCTOBER 2024: No. 1 no longer. The would-have-been groundbreaking study published in Nature Communications by Amit Goyal et al. claiming the world’s highest-performing high-temperature superconducting wires yet has been retracted by the authors.

The journal’s editorial statement that now accompanies the paper says that after publication, an error in the calculation of the reported performance was identified. All of the study’s authors agreed with the retraction.

The researchers were first alerted to the issue by Evgeny Talantsev at the Mikheev Institute of Metal Physics in Ekaterinburg, Russia, and Jeffery Tallon at the Victoria University of Wellington in New Zealand. In a 2015 study, the two researchers had suggested upper limits for thin-film superconductors, and Tallon notes follow-up papers showed these limits held for more than 100 known superconductors. “The Goyal paper claimed current densities 2.5 times higher, so it was immediately obvious to us that there was a problem here,” he says.

Upon request, Goyal and his colleagues “very kindly agreed to release their raw data and did so quickly,” Tallon says. He and Talantsev discovered a mistake in the conversion of magnetization units.

“Most people who had been in the game for a long time would be fully conversant with the units conversion because the instruments all deliver magnetic data in [centimeter-gram-second] gaussian units, so they always have to be converted to [the International System of Units],” Tallon says. “It has always been a little tricky, but students are asked to take great care and check their numbers against other reports to see if they agree.”

In a statement, Goyal notes he and his colleagues “intend to continue to push the field forward” by continuing to explore ways to enhance wire performance using nanostructural modifications. —Charles Q. Choi

Original article from 17 August, 2024 follows:

Superconductors have for decades spurred dreams of extraordinary technological breakthroughs, but many practical applications for them have remained out of reach. Now a new study reveals what may be the world’s highest-performing high-temperature superconducting wires yet, ones that carry 50 percent as much current as the previous record-holder. Scientists add this advance was achieved without increased costs or complexity to how superconducting wires are currently made.

Superconductors conduct electricity with zero resistance. Classic superconductors work only at super-cold temperatures below 30 degrees Kelvin. In contrast, high-temperature superconductors can operate at temperatures above 77 K, which means they can be cooled to superconductivity using comparatively inexpensive and less burdensome cryogenics built around liquid nitrogen coolant.

Regular electrical conductors all resist electron flow to some degree, resulting in wasted energy. The fact that superconductors conduct electricity without dissipating energy has long lead to dreams of significantly more efficient power grids. In addition, the way in which rivers of electric currents course through them means superconductors can serve as powerful electromagnets, for applications such as maglev trains, better MRI scanners for medicine, doubling the amount of power generated from wind turbines, and nuclear fusion power plants.

“Today, companies around the world are fabricating kilometer-long, high-temperature superconductor wires,” says Amit Goyal, SUNY Distinguished Professor and SUNY Empire Innovation Professor at the University of Buffalo in New York.

However, many large-scale applications for superconductors may stay fantasies until researchers can find a way to fabricate high-temperature superconducting wires in a more cost-effective manner.

In the new research, scientists have created wires that have set new records for the amount of current they can carry at temperatures ranging from 5 K to 77 K. Moreover, fabrication of the new wires requires processes no more complex or costly than those currently used to make high-temperature superconducting wires.

“The performance we have reported in 0.2-micron-thick wires is similar to wires almost 10 times thicker,” Goyal says.

At 4.2 K, the new wires carried 190 million amps per square centimeter without any externally applied magnetic field. This is some 50 percent better than results reported in 2022 and a full 100 percent better than ones detailed in 2021, Goyal and his colleagues note. At 20 K and under an externally applied magnetic field of 20 tesla—the kind of conditions envisioned for fusion applications—the new wires may carry about 9.3 million amps per square centimeter, roughly 5 times greater than present-day commercial high-temperature superconductor wires, they add.

Another factor key to the success of commercial high-temperature superconductor wires is pinning force—the ability to keep magnetic vortices pinned in place within the superconductors that could otherwise interfere with electron flow. (So in that sense higher pinning force values are better here—more conducive to the range of applications expected for such high-capacity, high-temperature superconductors.) The new wires showed record-setting pinning forces of more than 6.4 trillion newtons at 4.3 K under a 7 tesla magnetic field. This is more than twice as much as results previously reported in 2022.

The new wires are based on rare-earth barium copper oxide (REBCO). The wires use nanometer-sized columns of insulating, non-superconducting barium zirconate at nanometer-scale spacings within the superconductor that can help pin down magnetic vortices, allowing for higher supercurrents.

The researchers made these gains after a few years spent optimizing deposition processes, Goyal says. “We feel that high-temperature superconductor wire performance can still be significantly improved,” he adds. “We have several paths to get to better performance and will continue to explore these routes.”

Based on these results, high-temperature superconductor wire manufacturers “will hopefully further optimize their deposition conditions to improve the performance of their wires,” Goyal says. “Some companies may be able to do this in a short time.”

The hope is that superconductor companies will be able to significantly improve performance without too many changes to present-day manufacturing processes. “If high-temperature superconductor wire manufacturers can even just double the performance of commercial high-temperature superconductor wires while keeping capital equipment costs the same, it could make a transformative impact to the large-scale applications of superconductors,” Goyal says.

The scientists detailed their findings on 7 August in the journal Nature Communications.

This story was updated on 19 August 2024 to correct Amit Goyal’s title and affiliation.