A Further Understanding of Superconductivity
JUNE 10, 2013
A crucial ingredient of high-temperature superconductivity can be found in a class of materials that is entirely different than conventional superconductors. That discovery is the result of research by an international team of scientists working at the U.S. Department of Energy Office of Science’s Advanced Photon Source (APS).
“There have been more than 60,000 papers published on high-temperature superconductive material since its discovery in 1986,” said Jak Chakhalian, professor of physics at the University of Arkansas (UA) and a co-author of a new paper published on May 13, 2013, in Scientific Reports. “Unfortunately, as of today we have zero theoretical understanding of the mechanism behind this enigmatic phenomenon. In my mind, high-temperature superconductivity is the most important unsolved mystery of condensed matter physics.”
Superconductivity is a phenomenon that occurs in certain materials when cooled to extremely low temperatures such as -435° F. High temperature superconductivity occurs above -396 F, and has been seen up to -218 F in HgBa2Ca2Cu3O8. In both cases, electrical resistance drops to zero and complete expulsion of magnetic fields occurs.
Because superconductors have the ability to transport large electrical currents and produce high magnetic fields, they have long held great potential for electronic devices and power transmission.
The recent finding by a team of researchers from the University of Arkansas, the S.N. Bose National Centre for Basic Sciences (India), the University of Texas at Austin, the University of Tokyo (Japan), the Chinese Academy of Sciences, Argonne National Laboratory, and Nanyang Technological University (Singapore) is important to furthering our understanding of superconductivity, Chakhalian said.
In the mid-1980s, physicists determined that all high-temperature superconductive material must contain copper and oxygen, and those elements arrange two-dimensionally. Recently, superconductivity has been seen in other materials, such as the iron pnictides.
For this project, Chakhalian acquired complex oxides from the University of Texas in Austin. Chakhalian’s group conducted experiments on them utilizing the high-brightness x-rays from the X-ray Science Division 4-ID-C beamline at the Argonne National Laboratory APS to carry out soft x-ray absorption spectroscopy measurements.
Tanusri Saha-Dasgupta, Professor and Associate Dean at S.N. Bose National Centre, who with her doctoral student Swarnakamal Mukherjee carried out the theoretical calculations, said, “The theoretical study carried out in the work validates our experimental finding, giving us confidence on the further exploration of these compounds,”
Derek Meyers, a doctoral student in physics at the UA and the lead researcher on this study, found that the way electrons form in superconductive material—known as the Zhang-Rice singlet state—was present in a chemical compound that is very different from conventional superconductors.
“I can make a closed circuit out of the superconducting material, cool it down and attach a battery that starts the flow of the electrons. The current goes around the loop. Then I detach it and leave it. Hypothetically, 1 billion years later the flow of electrons is guaranteed to be exactly the same—with no losses,” Chakhalian said. “But the problem is we don’t know if we are even using it right. We have no microscopic understanding of what is behind it.
“There is now a whole different class of materials where you can search for the enigmatic superconductivity,” he said. “This is completely new because we know that the Zhang-Rice quantum state, which used to be the hallmark of this high-temperature superconductor, could be found in totally different crystal structures. Does it have a potential to become a novel superconductor? We don’t know, but it has all the right ingredients.”