Scientists Chart the Emergence of High-Temperature Superconductivity

November 19, 2012 04:19 PM EST By: Jennifer Rocha

New study reveals unexpected disappearance of superconducting fluctuations at super-cold temperatures

Story content courtesy of Brookhaven National Laboratory, US

The next generation of sustainable energy systems, from magnetic storage to offshore wind turbines, hinges in part on high-temperature superconductors (HTS), which can carry current with zero loss and perfect efficiency.

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and other collaborating institutions have discovered unexpected behavior that could be key to solving the HTS puzzle. Rising temperature always quenches (stops) superconductivity, but their new study reveals that extremely low temperatures can cause structural defects to produce a similar shutdown. This observation, which helps illuminate the murky emergence of superconductivity, could one day open the door for scientists to engineer inexpensive, high capacity, room-temperature superconductors.

In these HTS experiments, the scientists measured the flow of electricity to uncover the structure of the cuprate “canal.” The water volume corresponds to the density of electrons in the system, which, said study coauthor Ivan Bozovic, a physicist in Brookhaven Lab’s Condensed Matter Physics and Materials Science Department, was able to fine-tune with his custom atomic layer-by-layer molecular beam epitaxy (ALL-MBE) synthesis technique (see sidebar). While the films were atomically smooth, they contained deliberately built-in defects - randomly distributed strontium atoms. These imperfections act like “pits’ that can trap flowing electrons, rendering them immobile.

Probing this behavior further, the researchers not only discovered that the fluctuations vanish beyond that super-cold threshold, but that the trapping pattern subtly changes with each test. As it turns out, resistivity depends not just on temperature, but also on the material’s memory of its own history - how and where the electrons were previously trapped. This phenomenon, called hysteresis, strongly indicates that the underlying mechanism behind the superconductor-insulator transition is tied to electron localization.

“Understanding the origin and behavior of superconducting fluctuations gives us a greater understanding of how superconductivity emerges, and what can quench it,” Bozovic said. “Greater understanding, in turn, improves the chances to discover or design new and better superconductors.”

The research was funded by DOE’s Office of Science and the National Science Foundation Division of Materials Research, and featured additional collaborators from Florida State University, the University of Crete in Greece, and Nanyang Technical University in Singapore.


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