Rattled Atoms Mimic High-temperature Superconductivity

X-ray Laser Experiment Provides First Look at Changes in Atomic Structure that Support Superconductivity

An experiment at the Department of Energy’s SLAC National Accelerator Laboratory provided the first fleeting glimpse of the atomic structure of a material as it entered a state resembling room-temperature superconductivity – a long-sought phenomenon in which materials might conduct electricity with 100 percent efficiency under everyday conditions.

Researchers used a specific wavelength of laser light to rattle the atomic structure of a material called yttrium barium copper oxide, or YBCO. Then they probed the resulting changes in the structure with an X-ray laser beam from the Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility.

They discovered that the initial exposure to laser light triggered specific shifts in copper and oxygen atoms that squeezed and stretched the distances between them, creating a temporary alignment that exhibited signs of superconductivity for a few trillionths of a second at well above room temperature – up to 60 degrees Celsius (140 degrees Fahrenheit). The scientists coupled data from the experiment with theory to show how these changes in atomic positions allow a transfer of electrons that drives the superconductivity.

New Views of Atoms in Motion

“This is a highly interesting state, even though it only exists for a short period of time,” said Roman Mankowsky of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, who was lead author of a report on the experiment in the Dec. 4 print issue of Nature. “When the laser excites the material, it shifts the atoms and changes the structure. We hope these results will ultimately help in the design of new materials to enhance superconductivity.”

Sustaining such a state at room temperature would revolutionize many fields, making the electrical grid more efficient and enabling more powerful and compact computers. Traditional superconductors operate only at temperatures close to absolute zero. YBCO is one of a handful of materials discovered since 1986 that superconduct at somewhat higher temperatures; but they still have to be chilled to at least minus 135 degrees Celsius in order to sustain superconductivity, and scientists still don’t know what allows these so-called high-temperature superconductors to carry electricity with zero resistance.

A Powerful Tool for Exploring Superconductivity

Josh Turner, a SLAC staff scientist who has led other studies of YBCO at the LCLS, said powerful tools such as X-ray lasers have excited new interest in superconductor research by allowing researchers to isolate a specific property that they want to learn more about. This is important because high-temperature superconductors can exhibit a tangle of magnetic, electronic and structural properties that may compete or cooperate as the material moves toward a superconducting state. For example, another recently published LCLS study found that exciting YBCO with the same optical laser light disrupts an electronic order that competes with superconductivity.

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