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SLAC study suggests new phase of matter

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(ERIC KOFFMAN/The Stanford Daily)

Researchers at Stanford and the SLAC National Accelerator Laboratory may have discovered a new phase of matter, distinct from solids, gases, liquids and plasmas. Working in conjunction with scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and UC-Berkeley, the Stanford researchers made the discovery while studying certain properties of high-temperature superconductors.

The collaboration was organized by physics professor Zhi-Xun Shen, who is also a member of the Stanford Institute for Materials and Energy Science (SIMES) at SLAC. The team’s findings, co-authored by SLAC scientist Makoto Hashimoto and post-doctoral scholar Ruihua He, were published in the Mar. 25 issue of Science.

This recent research sheds new light on a well-established field. Superconductors conduct electricity with 100 percent efficiency, a property that gives them the potential to be a highly revolutionary technology. Hindering this potential, however, is the fact that they operate only at extremely low temperatures.

Scientists have tried to design “high-temperature” superconductors, which actually operate at room temperature and are of more practical use, but in the process have encountered a puzzling phenomenon. As electrons in the superconductor gain energy and change states due to the additional heat, the superconductors enter a unique electronic state that researchers term a “pseudogap.”

Many scientists have posited that the mysterious pseudogap, which has been inconclusively studied for some 20 years, merely represents a gradual transition to superconductivity. The Stanford team’s findings, however, suggest that the pseudogap may in fact be a new phase of matter because the electrons reorganize themselves into a distinct formation of their own–one that scientists have yet to fully understand.

“This work has the power to partially conclude a long-standing debate on the nature of the pseudogap phase, which is the central question to answer in high-temperature superconductivity–the unquestionable holy grail of modern condensed-matter physics,” He said.

“Our experiment suggests that proper management of this phase [the pseudogap] could be a critical step toward obtaining better superconductors that could have broad practical applicability,” Shen said.

The researchers used a three-pronged approach in investigating the pseudogap, combining different types of measurement to study electronic behavior at the material’s surface, thermodynamic behavior in its interior and changes to the electrons’ dynamic properties over time.

When electrons are superconducting, they pair up. This recent research revealed, however, that in the pseudogap, electrons do not pair up but rather reorganize into a unique formation. While these findings suggest that the pseudogap is more than just a transitional phase, they do not offer conclusive information on what such a formation means.

“I personally think it is a stretch to compare the phase that we found to the other four [phases],” He said. “But we are not the first to raise such a possibility.”

High-temperature superconductors are already being used in medical imaging, highly efficient energy generators and maglev trains, even though the warmest of them must be chilled halfway to absolute zero before they will superconduct. But this paper may be a breakthrough in better understanding superconductivity, perhaps paving the way for more practical technologies.