2007/06/29 by Kazuki Ohishi, K. Ohishi, R. H. Heffner +15
Physics and Astronomy · #Physics of Superconductivity and Magnetism #Rare-earth and actinide compounds #Superconductivity in MgB2 and Alloys #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.76.064504
11 pages
arxiv created 2007/06/29 · openalex publication_date 2007/08/06 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We have measured the temperature dependence and magnitude of the superfluid density \ensuremathρs(T) via the magnetic field penetration depth \ensuremathλ(T) in PuCoGa5 (nominal critical temperature Tc0=18.5\phantom\rule0.3em0exK) using the muon spin rotation technique in order to investigate the symmetry of the order parameter, and to study the effects of aging on the superconducting properties of a radioactive material. The same single crystals were measured after 25\phantom\rule0.3em0exdays (Tc=18.25\phantom\rule0.3em0exK) and 400\phantom\rule0.3em0exdays (Tc=15.0\phantom\rule0.3em0exK) of aging at room temperature. Penetration depths \ensuremathλ(0)=265(5) and \ensuremath\geqslant498(10)\phantom\rule0.3em0exnm are derived for the fresh and aged samples, respectively. The temperature dependence of the superfluid density \ensuremathρs(T)∕\ensuremathρs(0)=\ensuremathλ(0)2∕\ensuremathλ(T)2 is well described in both materials by a model using d-wave gap symmetry. Within the context of a strong-coupling dirty d-wave model a zero-temperature gap value \ensuremathΔ0=3.0kBTc0 is obtained in the fresh sample for a scattering rate \ensuremathΓ=0.005\ensuremathπkBTc0, which is consistent with Abrikosov-Gor'kov (AG) pair-breaking theory. This \ensuremathΔ0 should be compared to the weak-coupling value for a clean d-wave gap \ensuremathΔ0=2.14kBTc0. In the aged sample the same model yields \ensuremathΔ0=2.4kBTc0 for \ensuremathΓ=0.010\ensuremathπkBTc0. This value of \ensuremathΓ is much less than required by the AG pair-breaking formalism. Furthermore, the aged \ensuremathρs(0) is reduced by at least 70% compared to the fresh sample, which is also incompatible with \ensuremathΔTc∕Tc0\ensuremath∼20%, according to AG theory. We conclude that the data in aged PuCoGa5 support the postulate that the scattering from radiation-induced defects is not in the limit of the AG theory of an order parameter which is spatially averaged over impurity sites, but rather in the limit of short-coherence-length superconductivity. We show that a model calculation consistent with this assumption fits \ensuremathρs(T) in the aged sample rather well.