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Good Vibrations Make Magnesium Boride a Model Superconductor

MgB2
Image: courtesy of T. YILDIRIM/NIST

Early this past March, Japanese researchers described in Nature their discovery of a new and unexpected high-temperature superconductor, magnesium boride (MgB2). The material has since gained a great deal of attention, in no small part because it's cheap to make, easy to manipulate and superconducting at 39 K, which is much warmer than any other metal-containing superconductor.

Until recently, physicsts couldn't explain how MgB2 becomes superconducting at a temperature some 33 percent warmer than theory predicts. But two independent papers in Physical Review Letters now offer the remarkable answer: vibrations in the material's crystal lattice and its conducting electrons move in step, allowing the electrons to pass through the lattice undeterred¿much like partners who duck other couples' linked arms in a well-choreographed line dance.

Ray Osborne and colleagues at Argonne National Laboratories reported in the July 2nd PRL that electrons zipping past boron atoms in MgB2 quite easily "pluck" the crystal lattice, like a guitar string. The resulting vibration allows two electrons to form a so-called Cooper pair, which then travels resistance-free through the material. Another account in today's PRL from Jeff Lynn and Taner Yildirim at the National Institute of Standards and Technology and their colleagues confirms the earlier work. They further show just how perfectly coupled the lattice vibration is to the conducting electrons. The timing is so perfect, in fact, that the scientists say it will be hard to tweak the material to raise its superconducting temperature any higher.

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