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The discovery in 1996 of superconductivity at 0.2K near a magnetic
quantum phase transition in CeIn3 opened a new dynasty of
superconducting heavy electron materials, with many peculiar parallels
to cuprate superconductors. In 2000, the introduction of additional
layers of XIn2, led to the discovery of the so-called "115"
superconductors, with a tenfold increase in Tc. In 2002, the
replacement of Ce by Pu, drove the Tc up by an additional order of
magnitude to 18.5K. The recent discovery of a second material in this
family has further deepened the mystery.
In this talk I'll discuss the two newest "high temperature" heavy fermion superconductors in this series: PuCoGa5 and NpPd2Al5. These materials radically challenge the way we think about strongly correlated superconductivity. The way these materials directly transition from Curie paramagnets into anisotropic superconductors suggests a central role of spin as a driver for heavy electron superconductors - not just as the pairing glue - but as the basic fabric of the condensate. Motivated by these new materials, I'll discuss a model for superconductivity in the highest temperature superconductors in which the superconducting condensate involves formation of composite pairs between spins and conduction electrons. Using an extension of the symplectic N approach developed by Read and Sachdev, I'll show how the physics of superconductivity and the Kondo effect can be combined, giving rise to a composite pairing model for the new superconductors. |
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