SR measurements on the superconducting penetration depth in aged PuCoGa

Heffner, R. H.; Oishi, Kazuki; Higemoto, Wataru  ; Ito, Takashi   ; Morris, G. D.*; Fluss, M. J.*; MacLaughlin, D. E.*; Shu, L.*; Bauer, E. D.*; Sarrao, J. L.*

The superconductor PuCoGa possesses a relatively high critical temperature (T = 18.5 K), a moderate mass enhancement (Sommerfeld coefficient 80 mJ/mol-K and exhibits behavior consistent with spin-fluctuation-induced d-wave superconductivity. It is also radioactive, with its dominant radioisotope Pu having a half-life of 2.4 10 yrs. We report SR measurements of the temperature and field dependence of the magnetic field penetration depth (T,H) in a 400 day-old sample of PuCoGa (T = 15 K), and compare these results to data obtained on the same sample approximately one year earlier. In 600 Oe applied field both measurements show a linear low-temperature behavior for (T) - (0) = bT for T/T 0.5 with the same coefficient b. The magnitude of (0) in the aged sample has increased by a factor of about 1.8. The results are discussed in terms of the effects of radiation damage on the postulated d-wave superconducting order parameter.