In a discovery that reveals a whole new state of matter, research published in the journal Science shows that Cooper pairs, electronic duos that allow for superconductivity, can also conduct electricity as normal metals. [1
But in a new book published today (November 14, 2019) in Science a team of researchers showed that Cooper couples can also conduct electricity with some resistance, as ordinary metals do. The results describe an entirely new state of matter, according to the researchers, which will require a new theoretical explanation.
"There was evidence that this metallic state would occur in thin-film superconductors when cooled to their superconducting temperature, but whether or not Cooper couples participated in this state," says Jim Walts, professor of physics at Brown University and the corresponding author of the study. "We have developed a technique that allows us to test this issue and show that Cooper couples are indeed responsible for transporting a charge in this metallic state. Interestingly, no one is quite sure at the fundamental level how they do this, so this finding will require some more theoretical and experimental work to understand exactly what is happening. "
The Cooper couples were named after Leon Cooper, a Brown physics professor who won the Nobel Prize in 1972, to describe their role in providing superconductivity. Resistance is created when electrons travel in the atomic lattice of a material as they move. But when the electrons come together to become Cooper couples, they undergo a remarkable transformation. Electrons themselves are fermions, particles that obey the Pauli exclusion principle, which means that each electron tends to retain its own quantum state. Cooper pairs, however, act as bosons that can happily share the same condition. This bosonic behavior allows Cooper pairs to coordinate their movements with other sets of Cooper pairs in a way that reduces resistance to zero.
In 2007, Vales, working with Brown engineer and physics professor Jimmy Sue, showed that Cooper pairs can also produce insulation states as well as superconductivity. In very thin materials, instead of moving to a concert, couples are conspired to stay in place, strung together on small islands in material and unable to jump to the next island.
For this new study, Valles, Xu, and colleagues in China searched for Cooper pairs in a non-superconducting metallic state using a technique similar to that revealed for the Cooper couple isolators. The technique involves the modeling of a thin-film superconductor – in this case, high-temperature yttrium barium copper oxide (YBCO) superconductors – with small hole arrays. When the material has a current passing through it and is exposed to a magnetic field, the charge carriers in the material will circulate around the holes like water circulating in the sewer.
"We can measure the frequency at which these charges circulate," Vales said. "In this case, we found that the frequency is compatible with the fact that two electrons move at a time, not just one. So we can conclude that the charge carriers in this state are Cooper pairs, not single electrons. "
The idea that Cooper coupons are responsible for this metallic state is surprising, the researchers say, because there are elements of quantum theory that suggest that this should not be possible. So understanding only that, what happens in this state may lead to exciting new physics, but more research will be needed.
Fortunately, the researchers claim that the fact that this phenomenon was discovered in a high-temperature superconductor will make future research into Practical YBCO starts every day conductivity at about -181 degrees Celsius, and the metal phase starts at temperatures slightly above this, which is quite cold, but much warmer than other superconductors, which are active just above absolute zero . high temperature facilitates the use of spectroscopy and other techniques aimed at a better understanding of what is happening in this metal phase.
On the way, according to researchers, it may be possible to use this boson metal state for new types of electronic devices.
"The thing about bosons is that they're in a wavy state rather than electrons, so we're talking about them having a phase and disturbing the same way light does," Vales said. "So there may be new conditions for moving charge in devices through play with boson interference."
But for now, researchers are happy to find a new state of matter.
"Science is built on discoveries," said Sue, "and it's great that you found something completely new. "
Reference:" Intermediate boson metal state in the superconductor-insulator transition "by Chao Yang, Yi Liu, Yang Wang, Liu Feng, Qianmei He, Jian Sun, Yue Tang, Chunchun Wu, Jie Xiong, Wanli Zhang, Xi Lin, Hong Yao, Haiwen Liu, Gustavo Fernandes, Jimmy Xu, James M. Valles Jr., Jian Wang and Yanrong Li, November 14, 2019, Science .
Doi: 10.1126 / science.aax5798