Matthias J. Graf

On the interplay of small-moment magnetism and superconductivity in UPt3

The heavy-fermion compound UPt 3 is the prime candidate for unconventional superconductivity. Various Ginzburg—Landau models have been put forward in order to explain the unusual superconducting phase diagram with three vortex phases in the B—„ plane. The most perfected Ginzburg—Landau model is the E-representation model, in which the double superconducting transition in zero field, *„ # &0.05 K, is explained by the coupling of a vector superconducting order parameter to a symmetry-breaking field (SBF) e, where *„ # Je. The natural candidate for the SBF is the weak antiferromagnetically ordered moment m detected at „ N &6 K, with eJm2. By studying UPt 3 doped with small amounts of Pd it is possible to test the SBF model. We here report specific-heat experiments on single-crystalline samples, which show that *„ # increases upon doping. The results are compared to recent neutron-di⁄raction data, which reveal that m2 also increases upon Pd doping. The analysis of the data within the Ginzburg—Landau approach lends further support for the SBF model. ( 1998 Elsevier Science B.V. All rights reserved.