Anisotropic temperature dependence of the magnetic-field penetration in superconducting UPt3

The anisotropy and temperature dependence of the magnetic-field penetration in superconducting UPt3 have been measured by muon spin relaxation. The extrapolated zero-temperature values for the penetration depths parallel and perpendicular to the c axis are λ∥=7070±30 Å and λ⊥=7820±30 Å, respectively. The temperature dependences of λ∥ and λ⊥ are different and can both be accounted for by a superconducting gap function with a line of nodes in the basal plane and axial point nodes.