Muon spin rotation measurements of the superfluid density in fresh and aged superconducting PuCoGa{sub 5}

Journal Article · Wed Aug 01 00:00:00 EDT 2007 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.76.064504· OSTI ID:21055119

Ohishi, K; Higemoto, W ^[1]; Heffner, R H ^[1]; Morris, G D ^[2]; Bauer, E D; Graf, M J; Zhu, J -X; Morales, L A; Sarrao, J L ^[2]; Fluss, M J ^[3]; MacLaughlin, D E; Shu, L ^[4]; Ito, T U ^[1]

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1. Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)
2. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
3. Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States)
4. Department of Physics, University of California, Riverside, California 92521 (United States)

We have measured the temperature dependence and magnitude of the superfluid density {rho}{sub s}(T) via the magnetic field penetration depth {lambda}(T) in PuCoGa{sub 5} (nominal critical temperature T{sub c0}=18.5 K) 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 days (T{sub c}=18.25 K) and 400 days (T{sub c}=15.0 K) of aging at room temperature. Penetration depths {lambda}(0)=265(5) and {>=}498(10) nm are derived for the fresh and aged samples, respectively. The temperature dependence of the superfluid density {rho}{sub s}(T)/{rho}{sub s}(0)={lambda}(0){sup 2}/{lambda}(T){sup 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 {delta}{sub 0}=3.0k{sub B}T{sub c0} is obtained in the fresh sample for a scattering rate {gamma}=0.005{pi}k{sub B}T{sub c0}, which is consistent with Abrikosov-Gor'kov (AG) pair-breaking theory. This {delta}{sub 0} should be compared to the weak-coupling value for a clean d-wave gap {delta}{sub 0}=2.14k{sub B}T{sub c0}. In the aged sample the same model yields {delta}{sub 0}=2.4k{sub B}T{sub c0} for {gamma}=0.010{pi}k{sub B}T{sub c0}. This value of {gamma} is much less than required by the AG pair-breaking formalism. Furthermore, the aged {rho}{sub s}(0) is reduced by at least 70% compared to the fresh sample, which is also incompatible with {delta}T{sub c}/T{sub c0}{approx}20%, according to AG theory. We conclude that the data in aged PuCoGa{sub 5} 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 {rho}{sub s}(T) in the aged sample rather well.

• OSTI ID: 21055119
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 76, Issue 6; Other Information: DOI: 10.1103/PhysRevB.76.064504; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AGING
COBALT ALLOYS
COHERENCE LENGTH
CRITICAL TEMPERATURE
D WAVES
DENSITY
GALLIUM ALLOYS
MAGNETIC FIELDS
MONOCRYSTALS
MUON PROBES
MUON SPIN RELAXATION
ORDER PARAMETERS
PENETRATION DEPTH
PLUTONIUM ALLOYS
RADIOACTIVE MATERIALS
STRONG-COUPLING MODEL
SUPERCONDUCTIVITY
SUPERFLUIDITY
TEMPERATURE DEPENDENCE
TYPE-II SUPERCONDUCTORS