UNIAXIAL-STRESS ANISOTROPY OF THE DOUBLE SUPERCONDUCTING TRANSITION IN UPT3

We study the specific heat of single-crystal UPt3 for uniaxial stress 0 -less-than-or-equal-to S less-than-or-equal-to 4 kbar. For S parallel-to c, the lower and upper superconducting transitions move towards each other in temperature and merge by S = 2 kbar and T = 485 mK. In the normal state, the Sommerfeld constant-gamma increases 12% by 2 kbar and then plateaus. By contrast, for S parallel-to a, gamma-decreases steadily and the onset T(c)'s of the two superconducting transitions remain essentially unchanged, although the specific-heat peaks broaden markedly. Residual strain in the basal plane may account for some crystals of UPt3 showing only one broad superconducting transition.