μSRμSR studies of the superconducting order parameter in PuCoGa5PuCoGa5

We present transverse-field (TF) measurements of the in-plane magnetic-field penetration depth λ(T)λ(T) in single-crystalline PuCoGa5PuCoGa5 (Tc=18.5K) for 0.06T applied field (≈2–5×Hc1)(≈2–5×Hc1). We find that the temperature dependence of the superfluid density, and therefore Δλ(T)=λ(T)-λ(0)Δλ(T)=λ(T)-λ(0), is ∝T∝T for T/Tc⩽0.5T/Tc⩽0.5. We estimate that the measured λ(0)=241(3)nm. ZF measurements find no evidence for time-reversal symmetry violation. The ZF and TF measurements are consistent with an even-parity (pseudo-spin singlet), d-wave pairing state.