Superconductivity in heavy-fermion U(Pt,Pd)(3) and its interplay with magnetism

The effect of Pd doping on the superconducting phase diagram of the unconve ntional superconductor UPt3 has been measured by (magneto)resistance, speci fic heat, thermal expansion, and magnetostriction. Experiment on single- an d polycrystalline U(Pt1-xPdx)(3) for x less than or equal to 0.006 show tha t the superconducting transition temperatures of the A phase T-c(+), and of the B phase T-c(-) both decrease, while the splitting Delta T-c increases at a rate of 0.30+/-0.02 K/at. % Pd. The B phase is suppressed first, near x=0.004, while the A phase survives until x congruent to 0.007. We find tha t Delta T-c(x) correlates with an increase of the weak magnetic moment m(x) upon Pd doping. This provides further evidence for Ginzburg-Landau scenari os with magnetism as the symmetry-breaking field, i.e., the two-dimensional (2D) E representation and the 1D odd-parity model. Only for small splittin gs Delta T(c)(proportional to)m(2)(T-c(+)) (Delta T(c)less than or equal to 0.05 K) as predicted. The results at larger splittings call for Ginzburg-L andau expansions beyond fourth order. The tetracritical point in the B-T pl ane persists until at least x=0.002 for B perpendicular to c, while it is r apidly suppressed for B parallel to c. Upon alloying the A and B phases gai n stability at the expense of the C phase. [S0163-1829(99)01638-0].