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The Search for Complex Order Parameter Symmetry in Unconventional Superconductors

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Whitfield Lecture by Dale Van Harlingen from University of Illinois at Urbana-Champaign
When
09 October 2008 from 4:00 PM to 5:00 PM
Where
117 Osmond Laboratory
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One of the significant testable predictions of the BCS theory of superconductivity was the presence of an energy gap and all conventional superconductors were found to exhibit an isotropic “s-wave” pairing symmetry. However, the discovery of the high-temperature superconductors in the 1980’s revealed the existence of materials that were suspected to have unconventional order parameter symmetry characterized by anisotropies in the magnitude and/or phase. In this talk, I will describe the technique of Josephson interferometry and review how it was implemented in several manifestations to verify that the high temperature cuprates had a dx2-y2 pairing symmetry. I will then describe our ongoing quest to identify superconductors with complex order parameters that exhibit broken time-reversal symmetry. Our experiments give strong evidence for dynamical chiral p-wave order parameter domains of the form pxipy in the ruthenate superconductor Sr2RuO4, and a three-dimensional complex state in the heavy fermion superconductor UPt3 which exhibits two superconductor phases. In addition to exhibiting exciting new physics, complex superconductors have potential application for topologically-protected quantum computing.

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