Muon spin relaxation in the heavy fermion system UPt3

We report muon spin rotation/relaxation (μSR) measurements of the heavy fermion superconductor UPt3 in external fields Hext∥ĉ. We find that the muon Knight shift is unchanged in the superconducting state, consistent with odd-parity pairing (such as p wave). The transverse field relaxation is observed to be strongly field dependent, decreasing with increasing field. Below Tc the increase is barely detectable in an applied field of 4 kG∥ĉ. On the basis of the high field measurements, we estimate the low temperature penetration depth to be λ(T→0)≥ (R18)11 000 Å.