Condensed-Matter Physics & Materials Science Seminar

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_2Al_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) {\bf 420}, 297-299 (2002).
[3] Rebecca Flint, M. Dzero, P. Coleman, "Heavy electrons and the symplectic symmetry of spin.", Nature Ph