A recent study published in the Journal Science has revealed an entirely new state of matter. Cooper pairs, electron duos that enable superconductivity have been found to be able to conduct electricity, just as normal metals do.
Cooper pairs show two abilities. They glide freely, creating a superconducting state, or an insulating state when they get stuck inside a material, unable to move at all.
Cooper Pairs were named in honor of Leon Cooper, a researcher at Brown who won the 1972 Nobel Prize for demonstrating their role in enabling superconductivity.
Now, a new study published in Science has revealed that Cooper pairs can also conduct electricity with a certain amount of resistance, as normal metals do. And this will require a new theoretical explanation; a new state of matter.
“There had been evidence that this metallic state would arise in thin-film superconductors as they were cooled down toward their superconducting temperature, but whether or not that state involved Cooper pairs was an open question,” explained Jim Valles, a professor of physics at Brown University and the study’s corresponding author.
“We’ve developed a technique that enables us to test that question and we showed that, indeed, Cooper pairs are responsible for transporting charge in this metallic state. What’s interesting is that no one is quite sure at a fundamental level how they do that, so this finding will require some more theoretical and experimental work to understand exactly what’s happening.”
Resistance is produced when electrons rattle in the atomic network of a material as they move. But when electrons bond to become Cooper pairs, they undergo a remarkable transformation.
The electrons themselves are fermions, particles that obey Pauli’s exclusion principle, which means that each electron tends to maintain its own quantum state.
Cooper pairs, however, act like bosons, who can share the same state.
That bosonic behavior allows Cooper pairs to coordinate their movements with other sets of Cooper pairs in a way that reduces resistance to zero.
Previous studies have shown that Cooper pairs also had the ability to create an insulating state as well as superconductivity. In extremely thin materials, instead of moving in concert the pairs stay in one place, stranded on small islands within a material and are unable to move to the next island.
The new study saw Valles and Jimmy Xu look for Cooper pairs in a non-superconducting metallic state using a technique similar to that which revealed Cooper pair insulators.
The technique consists in designing a thin-film superconductor, in this case, a high-temperature superconductor yttrium barium copper oxide (YBCO), with a series of small holes.
When the material has current through it and is exposed to a magnetic field, the charge carriers in the material will encircle the holes like the water surrounding a drain.
“We can measure the frequency at which these charges circle,” Valles explained.
“In this case, we found that the frequency is consistent with there being two electrons going around at a time instead of just one. So we can conclude that the charge carriers in this state are Cooper pairs and not single electrons.”