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Composite pairing in the new "high Tc" Heavy Fermion Superconductors


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 XIn 2 , led to the discovery of the so-called "115" superconductors, with a tenfold increase in Tc[1].  By 2002, the replacement of Ce by Pu, drove the Tc up by an additional order of magnitude to 18.5K[2].  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 NpPd 2 Al 5 . 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[3]. Using this idea, we'll discuss how the physics of superconductivity and the Kondo effect can be combined, giving rise to a composite pairing model for the new superconductors.

[1] H. Hegger, C. Petrovic, E. G. Moshopoulou, M. F. Hundley, J. L. Sarrao, Z. Fisk, and J. D. Thompson, ''Pressure-Induced Superconductivity in Quasi-2D CeRhIn 5 '' Phys. Rev. Lett. 84 , 4986-4989 (2000).

[2] J. L. Sarrao  et al. , “Plutonium-based superconductivity with a transition temperature above 18 K", Nature (London) 420 , 297-299 (2002).

[3] Rebecca Flint, M. Dzero, P. Coleman, "Heavy electrons and the symplectic symmetry of spin", Nature Physics 4 , 643 - 648 (2008).