Scientists seeking to understand the intricacies of high-temperature superconductivity -- the ability of certain materials to carry electrical current with no energy loss -- have been particularly puzzled by a mysterious phase that emerges as charge carriers are added that appears to compete with superconductivity. It's also been a mystery why, within this "pseudogap" phase, the movement of superconducting electrons appears to be restricted to certain directions. Detailed studies of a material as it transforms from an insulator through the “pseudogap" into a full-blown superconductor links two “personality” changes of electrons at a critical point.
Now, a team lead by scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Cornell University have used unique capabilities to reveal detailed characteristics of the electrons in one of these materials as it transforms from an insulator through the mysterious pseudogap phase and eventually into a full-blown superconductor. The results, described in the May 9, 2014, issue of Science, link two distinct personality changes in the material's electrons: the disappearance of a rather exotic periodic static arrangement of certain electrons within the pseudogap phase, and the sudden ability of all the material's electrons to move freely in any direction. The finding strengthens support for the idea that the periodic arrangement -- variously referred to as "stripes" or "density waves" -- restricts the flow of electrons and impairs maximal superconductivity in the pseudogap phase.
"This is the first time an experiment has directly linked the disappearance of the density waves and their associated nanoscale crystal distortions with the emergence of universally free-flowing electrons needed for unrestricted superconductivity," said lead author J.C. Séamus Davis, a senior physicist and Director of DOE's Center for Emergent Superconductivity at Brookhaven Lab and also a professor at both Cornell University and the St. Andrews University in Scotland. "These new measurements finally show us why, in the mysterious pseudogap state of this material, the electrons are less free to move."
That information, in turn, may help scientists engineer ways to get superconductivity flowing under more favorable conditions. Right now, even these "high-temperature" copper-oxide materials operate as superconductors only when cooled to below -100 degrees Celsius. "That's room temperature during a particularly bad winter in Antarctica," Davis said. The hope is to find ways to raise the operating temperature for real-world energy-saving applications -- things like highly efficient power generation and transmission and computers that work at speeds thousands of times faster than today's.