Systematic Investigation of the Superconducting Behavior in Aged PuCoGa 5
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0986-OO02-02
Systematic Investigation of the Superconducting Behavior in Aged PuCoGa5 Frédéric Jutier, Eric Colineau, Jean-Christophe Griveau, Jean Rebizant, and Franck Wastin European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, Karlsruhe, D76125, Germany ABSTRACT In this work, we have undertaken to follow the evolution of the PuCoGa5 superconducting behavior as a function of the damages created by self-radiation effects induced from the Pu-decay. It is shown that the critical temperature is particularly sensitive with ageing. Ageing effects on fundamental parameters such as the lattice parameters of the PuCoGa5 and the electrical resistivity provide some new hints of the unconventional character of the superconductivity in this class of materials.
INTRODUCTION The discoveries of superconductivity at Tc = 18.5 K in PuCoGa5 [1] and Tc = 9.5 K in PuRhGa5 [2] have lead to a substantial impact given the nearly order-of-magnitude larger Tc than any other f-electron intermetallic. Not only are these the first Pu-based superconductors, but also several of their features reveal both localized and itinerant f-electron behavior suggesting a “dual-nature” of Pu. On the one hand, with nearest f-f spacings well beyond the Hill limit and Curie-Weiss-like magnetic susceptibilities, these Pu-based superconductors appear to have localized 5f electrons. On the other hand, their enhanced Sommerfeld coefficients, γ ≈ 100 mJ/mol-K2, and BCS-like jump ∆C/γTc, are consistent with bulk superconductivity developing out of a relatively narrow, correlated band of conduction electrons [2-4]. Although this picture of Pu’s 5f dual character may still leave open the possibility that superconductivity is conventional, power-laws in specific heat [3] and, most convincingly, in the spin-lattice relaxation rate 1/T1 well below Tc of PuCoGa5 [5] and PuRhGa5 [6] argue strongly for a superconducting gap with nodes. The most accepted picture establishes spin-singlet pairing in PuCoGa5, similar to what was evidenced in the isostructural heavy-fermion superconductor CeCoIn5, and the formation of an unconventional superconducting state favored by low-energy antiferromagnetic spin fluctuations [7]. While the nature of the 5f electrons remains poorly understood in these systems mainly because Pu is much more radioactive than U and its self-heating makes it difficult to study properties at temperatures much less than 4 K (
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