Physicists at the University of Illinois at Chicago have identified the “quantum glue” that binds electrons together to evoke superconductivity in a crucial step towards the creation of high-speed energy transport methods that conduct electricity without current loss.
The new research, published online in the Proceedings of the National Academy of Sciences, is a collaboration between a team of theoretical physicists led by Dirk Morr, professor of physics at the University of Illinois at Chicago, and experimentalists led by Seamus J.C. Davis of Cornell University and Brookhaven National Laboratory.
Scientists have long studied superconducting materials in an effort to harness their unique properties. Though the earliest superconducting materials only functioned in extremely cold operating temperatures near absolute zero, or −459.67 degrees Fahrenheit, researchers have since discovered newer high-temperature superconductors that work at slightly elevated temperatures. These unconventional materials are believed to work differently compared to the earlier superconductors, and scientists are hopeful further research may lead to room-temperature superconductors that can be used to create faster methods of transferring energy without the associated loss.
According to a UIC press release, two researchers in Davis’ group, Freek Massee and Milan Allan, examined an unconventional superconductor known as CeCoIn5, which consists of cerium, cobalt and indium. Using new theoretical framework developed at UIC by Morr and graduate student John Van Dyke to analyze the data, the team identified magnetism as the force causing the material’s superconductivity.
“For a long time, we were unable to develop a detailed theoretical understanding of this unconventional superconductor,” Morr said, explaining that two crucial insights into the complex electronic structure of CeCoIn5 had been missing—the relationship between the momentum and energy of electrons moving through the material, and the phenomenon that binds these electrons into a Cooper pair to elicit superconductivity. However, the high-precision measurements of CeCoIn5 taken by the Davis group using a technique known as quasi-particle interference spectroscopy, combined with the UIC-developed theoretical framework, allowed the researchers to gain new insight.
Because magnetism is highly directional, “knowing the directional dependence of the quantum glue, we were able, for the first time, to quantitatively predict the material’s superconducting properties using a series of mathematical equations,” Morr said. These calculations, he explained, “showed that the gap possesses what’s called a d-wave symmetry, implying that for certain directions the electrons were bound together very strongly, while they were not bound at all for other directions.” Directional dependence is considered one of the key elements of unconventional superconductors.
From this research, Morr says, the team concluded that magnetism is the cause of the emergence of unconventional superconductivity in CeCoIn5.
“We now have an excellent starting point to explore how superconductivity works in other complex material,” Morr said. “With a working theory, we can now investigate how we have to tweak the system to raise the critical temperature—ideally, all the way up to room temperature.”
