PuCoGa5:
Dazed and confused superconducting 5f electrons?
Eric D. Bauer
The
discovery of superconductivity in PuCoGa5 with a transition temperature of Tc =
18.5 K has generated renewed interest in Pu-based intermetallic compounds [1].
PuCoGa5, and its superconducting cousin PuRhGa5 (Tc=8.7 K), have the same
crystal structure as a growing class of tetragonal CemTnIn2m+3n (T=Co, Rh, Ir) heavy
fermion superconductors, suggesting that the structure plays a key role in
generating superconductivity in these materials. The Pu 5f electrons in
PuCoGa5 appear to be neither fully localized nor fully itinerant; elements of
both kinds of behavior manifest themselves in photoemission measurements [2]
and in physical properties such as an enhanced electronic specific heat
coefficient ~ 100 mJ/mol-K2 consistent with moderately heavy fermion
behavior. Nuclear magnetic resonance measurements [3] provide strong evidence
for unconventional d-wave superconductivity that is mediated by magnetic
(spin) fluctuations rather than by phonons in the case of conventional
superconductors such as Al. While similar measurements have firmly established
that the CeTIn5 compounds are unconventional d-wave superconductors,
most probably mediated by antiferromagnetic spin fluctuations, it is less clear
what the origin of superconductivity is in PuCoGa5. In this talk, I will
discuss recent measurements on PuCoGa5 that elucidate the nature of
superconductivity, spin fluctuations, and its 5f electrons.