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In this issue:
SIMES Physicists Demystify Electron Behavior in High-temperature Superconductors
Beam Is Back in the LHC

SLAC Today

Tuesday - October 27, 2009

SIMES Physicists Demystify Electron Behavior in High-temperature Superconductors

 (Image: Symmetry magazine.)

Researchers at the Stanford Institute for Materials and Energy Science, a joint institute of SLAC and Stanford University, have found encouraging evidence to help explain the mysterious behavior of electrons in "unconventional" high-temperature superconductors. In an article published last week in Nature Physics, SIMES researcher and Stanford Professor Martin Greven and his team show a simple relationship that may help explain some key properties of unconventional superconductors. Research on such materials could impact further studies for practical uses in superconducting magnets and wires that transmit electricity without energy loss.

"The article shows a leap of insight gained based on our prior experimental work and seeing how it fits in with everything else we already know about other unconventional superconductors," said Greven, who together with co-author Guichuan Yu is now transitioning to a new post at the University of Minnesota. The paper is the culmination of research projects led by then Stanford graduate student Yu, investigating the properties of two unconventional superconductors, which operate at higher temperatures than their supercold conventional counterparts.

Superconductivity is a low-temperature phenomenon in certain materials that is characterized by zero electrical resistance. It relies on unusual collective behavior of electrons, which pair together to move freely without energy-sapping interactions. In conventional low-temperature superconductors, electrons pair as a result of their interaction with the vibrations of a crystal lattice, the ordered arrangement of atoms in many superconducting materials. An electron moving in one direction causes a vibration in the lattice, like an insect walking across a spider web. An electron moving in the opposite direction detects these vibrations and combines with the first electron, forming what physicists call a Cooper pair.

In unconventional superconductors, however, significant electronic and magnetic interactions, rather than vibrations, seem to cause electron pairing. "What glues electrons into Cooper pairs in these materials has been an open question, but one promising answer is magnetic effects," Greven said.  Read more...

Beam Is Back in the LHC

CERN reports that beams of protons and lead ions were injected into the Large Hadron Collider this weekend. The beams made a partial tour of the LHC in both directions before being dumped. This marks the first time in more than a year that particles have entered the LHC, and the first time ever that lead ions traveled through part of the LHC.

On Friday, protons and lead ions traveled clockwise through the LHC, passing through the ALICE detector before being dumped. On Saturday, protons traveled counterclockwise through the LHCb detector. These injection tests allow the scientists and engineers working on the LHC to check that the various sectors are prepared for the particle beam and that the beam is stable. Rama Calaga of Brookhaven National Laboratory was among the scientists monitoring the tests. Calaga noted that these tests were "a spectacular success and there were no surprises."

The CERN news item also has a photo of the first beam of lead ions entering the LHC.

This story originally appeared in Symmetry Breaking.

For more news, see also:

Particles Are Back in the LHC! LHC news release

Particle Beams Injected into the LHC BBC News

LHC home page at CERN

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