Truce: Experiment reveals coexistence between competing states

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By Roger Snodgrass

Scientists at Los Alamos National Laboratory, working with an international team of collaborators, have reported a curious scientific phenomenon that seems to defy conventional explanations.

This peculiar situation has emerged in a series of steps over the last several years. It involves superconductivity and magnetism, well-known rival states of matter that have now been found under certain precise conditions to get along very well.

Superconductivity is a material state that exhibits zero electrical resistance and has been typically defined by its impermeability to a magnetic field.

But now a report in the Aug. 21 ScienceXpress, an advance electronic print of selected papers for publication in the journal Science, discloses that on certain carefully arranged occasions, the two states actually depend on each other.

“This co-existence is an exotic superconducting state that has not been observed in any other superconducting material,” said Roman Movshovich in a laboratory announcement.

“Such a new and unexpected result has taken the community by surprise,” said Joe D. Thompson, a specialist in cold temperature materials. “In response to some of the talks, listeners opened their mouths and nothing came out.”

Movshovich, Thompson and Eric Bauer, who synthesized the superconducting crystals used in the experiment, are three of the LANL scientists who were co-authors of the paper.

“It’s up to Eric to make the materials and Roman to make the measurements, and me to watch,” Thompson said this week. Bauer said later that Thompson was a critical part of the interpretive process.

A fourth participant from the lab was John Sarrao, whose work in plutonium superconductivity is directly related to the discoveries.

Altogether, there were 11 co-authors of the paper, including four Swiss scientists. Final measurements using a neutron beam were made in Switzerland.

“These are non-trivial experiments,” said Movshovich, “which is why there are so many authors.”

The new findings have been on the tip of researchers’ awareness for several years. They have established that there is a “rich interplay” between superconductivity and magnetism, but now for the first time the research team has pinpointed the ‘Q phase,’ a sliver of correspondence between a high magnetic field and low temperature where “superconductivity and magnetic order co-exist, but the character of the superconducting state could not be ascertained,” as they state, “Coupled Superconducting and Magnetic Order in CeCoIn.”

A new and mysterious set of circumstances in the superconducting arena is especially welcome, because the mechanisms by which the phenomena occur are so poorly understood, and while temperatures for achieving superconductivity have crept slightly higher, they are still hundreds of degrees below zero.

“This discovery has brought physicists one step closer to get to grips with superconductivity at high temperatures,” said another of the lead authors, Andrea Bianchi, a former postdoctoral researcher at Los Alamos, now at the University of Montreal. “Until now physicists were going around in circles. This discovery is unambiguous because it was made in a clean superconductor and it is a big boost toward the understanding of unconventional superconductivity.”

The practical implications of finding a new angle on the subatomic mechanisms by which superconductivity works are widely anticipated. Even a new exotic mechanism wouldn’t be turned away.

In a world that needs an energy boost, finding a way to transmit efficient electrical current at room temperatures would have many applications: power savings for magnetically levitated trains, communications, computing devices, medical equipment, generators and the electric grid connecting power plants to homes and offices.

“It’s important to understand a new state of material, but the knowledge gained may also be applied to other systems,” said Movshovich, looking forward to a number of interesting experiments to come and “a very exciting time.”