THERMODYNAMICS OF SUPERCONDUCTING UPT(3) UNDER UNIAXIAL PRESSURE

From the theory of Yip, Li, and Kumar, we derive convenient expression s relating the slopes of the phase boundaries near the tetracritical p oint (TP) in the superconducting heavy-fermion compound UPt3 to the ju mps in the specific heat across the transitions. We apply these relati ons to our recent measurements on the pressure dependence of the phase boundaries near the TP for magnetic field, H, parallel to both the a and c axes. Comparison with published data on the specific heat jumps at zero pressure or at zero field implies that the low-field inner tra nsition line is first order for the field orientation H parallel-to a for H > O, and is likely to be second order for H parallel-to c. For H = O the corresponding transition line in the pressure-temperature pla ne is likely to be second order as well.