Temperature superconductor gives fascinating possibilities – 03/16/2023 – Science

Scientists last week announced a spectacular breakthrough towards the dream of a material capable of transmitting electricity effortlessly in everyday conditions. Such a breakthrough could transform virtually any technology that uses electrical energy, opening up new possibilities for telephones, magnetic levitation trains and fusion power plants.

Normally, the flow of electricity encounters resistance as it moves through the wires, almost like a kind of friction, and some of the energy is lost as heat. A century ago, physicists discovered materials, now called superconductors, in which electrical resistance seemed to magically disappear. But these materials only lost their strength at extremely cold temperatures, which limited practical applications. For decades, scientists have searched for superconductors that work at room temperature.

Last week’s announcement is the latest attempt in that direction, but it comes from a team that faces widespread distrust because a paper of theirs from 2020 that described a promising but less practical superconducting material was retracted (withdrawn) after other scientists questioned some data. .

The new superconductor consists of lutetium and hydrogen with a little bit of nitrogen mixed in. It needs to be compressed to a pressure of 145,000 pounds per square inch before it gains its superconducting capability. That’s about ten times the pressure exerted on the bottom of the deepest ocean trenches.

But it’s also less than a hundredth of what the 2020 result called for, which was similar to crushing forces found several thousand kilometers deep in Earth. This suggests that further investigation of the material could lead to a superconductor that works at room temperature and at normal atmospheric pressure of 14.7 pounds per square inch (1 atm).

“This is the beginning of the new type of material that is useful for practical applications”, said Ranga P. Dias, professor of mechanical engineering and physics at the University of Rochester, in New York, to a crowded room of scientists on the last day 7 in a American Physical Society meeting in Las Vegas.

A more complete account of his team’s findings was published on the 8th in the journal Nature, the same one that published and portrayed the findings in 2020.

Rochester’s team started with a small, thin sheet of lutetium, a silvery-white metal that is among the rarest rare-earth elements, and pressed it between two interlocking diamonds. A gas of 99% hydrogen and 1% nitrogen was then pumped into the small chamber and compressed to high pressure. The sample was heated overnight at 150 degrees Fahrenheit (65.5 °C) and after 24 hours the pressure was released.

About a third of the time, the process produced the desired result: a small, vibrant blue crystal. “Injecting nitrogen to make lutetium hydride is not so easy,” said Dias.

In one of the University of Rochester laboratories used by Dias’ group, graduate student Hiranya Pasan demonstrated the material’s surprising hue-changing property during a reporter’s visit last week. As the screws were tightened to increase pressure, the blue turned to a reddish hue.

“It’s very pink,” Dias said. At even higher pressures, he said, “it gets to a bright red.”

In the paper, the researchers reported that the pink crystals exhibited key superconducting properties, such as zero resistance, at temperatures up to 70 degrees Fahrenheit (21°C).

“I’m cautiously optimistic,” said Timothy Strobel, a scientist at the Carnegie Institution for Science in Washington who was not involved in Dias’s study. “The published data looks great.”

“If this is real, it’s a really important advance,” said Paul CW Chu, a professor of physics at the University of Houston, who was also not involved in the research.

However, the “if” part of this sentiment revolves around Dias, who has been dogged by doubts and criticism, and even accusations by some scientists that he fabricated certain data. The results of the 2020 Nature paper have yet to be replicated by other researchers, and critics say Dias was slow to allow others to look at his data or perform independent analyzes of his superconductors.

Nature’s editors retracted the earlier paper last year, over objections from Dias and the other authors.

“I’ve lost a little bit of confidence in what’s coming out of this group,” said James Hamlin, a professor of physics at the University of Florida.

However, the new article went through the peer review process in the same journal.

Under pressure

Superconductivity was discovered by Dutch physicist Heike Kamerlingh Onnes and his team in 1911. Not only do superconductors carry electricity with essentially zero electrical resistance, they also have the strange ability known as the Meissner effect, which guarantees zero magnetic field inside the material.

The first known superconductors required temperatures just a few degrees above absolute zero, or minus 459.67 degrees Fahrenheit. In the 1980s, physicists discovered so-called high-temperature superconductors, but even they became superconductors under conditions much colder than those encountered in everyday use.

The standard theory explaining superconductivity predicts that hydrogen should be a superconductor at higher temperatures if it could be compressed tightly enough. But even the toughest of diamonds breaks before reaching pressures of this magnitude. Scientists began looking at hydrogen mixed with another element, surmising that the chemical bonds might help squeeze the hydrogen atoms together.

In the research described in the retracted 2020 article, Dias’ group used hydrogen, sulfur and carbon. With three elements, the scientists said, they were able to tweak the electronic properties of the compound to achieve a higher superconducting temperature.

Not everyone believed this, however.

Dias’ main antagonist is Jorge Hirsch, a theoretical physicist at the University of California, San Diego. He focused on measurements that Dias’ group had made of the carbon-sulfur-hydrogen compound’s response to oscillating magnetic fields, evidence of the Meissner effect. The script in the post looked too tidy, and the scientists didn’t explain how they subtracted background effects.

When Dias released the underlying raw data, Hirsch claimed, his analysis indicated that it had been generated by a mathematical formula and really couldn’t be measured in an experiment. “From a measurement, you don’t get analytical formulas,” Hirsch said. “You get numbers with noise.”

His complaints about Dias became so persistent and strident that others in the field circulated a letter complaining about decades of disturbing behavior by Hirsch.

Hirsch is a denier of the BCS theory, which was developed in 1957 by three physicists –John Bardeen, Leon N. Cooper and J. Robert Schrieffer– to explain how superconductivity works. The BCS, he said, is in many ways “a lie”, unable to explain the Meissner effect. He offered his own alternative explanation.

Notably, Hirsch has said that there can be no superconductivity in any of these high-pressure materials because hydrogen cannot be a superconductor. He gained few allies.

As the new lutetium-based material is superconducting at much lower pressures, many other research groups will be able to try to replicate the experiment. Dias said he wanted to give a more precise recipe for how to make the compost and share samples, but first he needs to resolve intellectual property issues. He founded the company Unearthly Materials, which plans to turn research into profit.

Strobel said he would start work as soon as he got back from the Las Vegas conference. “We can have a result literally in one day,” he said.

Hirsch also said he hoped the responses would come quickly. “If this is right, it will prove my work for the past 35 years wrong,” he said. “Which would make me very happy, because then I would know.”

“But I think I’m right and this is wrong,” added Hirsch.

Translated by Luiz Roberto M. Gonçalves