Critical fields and Landau-Ginzburg parameters of the heavy-fermion superconductor UPt3

Measurements of both the lower and upper critical fields along all three principal axes of the heavy-fermion superconductor UPt3 have been performed. A kink in the temperature dependence of the lower critical field, Hc1, is observed for all three orientations, which is in agreement with a recent theory by Hess, Tokuyasu, and Sauls. Also, an anisotropy of the temperature dependence of the lower critical field is observed at low temperatures (T<290 mK). The Landau-Ginzburg parameters are estimated from the experimental results.