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  • SRC Newsflash

    Kaminski and colleagues publish paper on momentum dependence of the superconducting gap in NdFeAsO0.9F0.1 single crystals measured by angle resolved photoemission spectroscopy.

    Classical superconductors rely on phonon mechanism and Tc is limited to ~25K. In 1986 high temperature superconductivity was discovered in cuprates (compounds based on copper oxide) with Tc~130K which allows for use of liquid nitrogen for cooling and wider practical applications. They have very peculiar properties with gap symmetry very different from classical superconductors (d-wave vs. s-wave). For 20 years people thought that there is something special about cuprates and only copper can lead to high temperature superconductivity.

    This year superconductivity was discovered in NdFeAsOF with Tc~50K - compound with no copper and even more surprising it contains Fe, which is normally magnetic (thought to be bad for superconductivity). So these materials break the "tyranny" of copper in high temperature superconductivity. Even better, another related material was discovered—BaKFe2As2—and does not contain oxygen. Of course, there is question whether the mechanism here is the same as the classical (unlikely because of high Tc), the same as in cuprates, or something entirely new.

    We measured the symmetry of gap in NdFeAsO0.9F0.1 at the Synchrotron Radiation Center (University of Wisconsin) and found it to be isotropic (more s-wave than d-wave), thus probably not related to the mechanism in cuprates—therefore it appears like there is a third mechanism for getting superconductivity at unusually high temperatures.

    Phys. Rev. Lett. 101, 147003 (2008)