µSR Studies of Pu Metal and the Pu-based Superconductor PuCoGa5

Abstract

We present recent measurements of the magnetic properties of Pu metal and the superconducting properties of PuCoGa 5 using the µSR technique. Our measurements set the most stringent upper limits to date on the magnitude of the ordered moments µ ord in α-Pu and δ-stabilized Pu (alloyed with 4.3 at. % Ga) in zero applied field: µ ord ≤10 -3 µ B at T \cong4 K. Measurements of the in-plane magnetic-field penetration depth λ( T ) in PuCoGa 5 ( T c =18.5 K) for 0.06 T applied field (≈2-5 × H c1 ) show that the temperature dependence of the superfluid density, and therefore Δλ( T )=λ( T )-λ(0), are ∝ T for T / T c ≤0.5. We estimate that λ(0)=241(3) nm. We also find no evidence for a time-reversal-symmetry violating superconducting order parameter. Taken together the measurements in PuCoGa 5 are, therefore, consistent with an even-parity (pseudo-spin singlet), d-wave pairing state.