Magnetic Penetration Depth and Pairing State of UPt sub 3

Using the technique of muon-spin-rotation (mu sup + SR), we have investigated the magnetic penetration depth in single-crystal UPt sub 3 for applied fields along the c- and a- directions. The data indicate a characteristic penetration depth of lambda sub (ab) (0) ~ lambda sub (bc) (0) ~ 8x10 sup 3 angstroms. For H//c, our data show a linear T-dependence of sigma which is consistent with the existence of lines of nodes in the gap function corresponding to a polar-like superconducting state. Alternatively for H//a, the T-dependence of sigma is somewhat stronger than linear. The anisotropy allows us to distinguish between current theories predicting the gap structure of UPt sub 3.