In this paper we study the thermodynamics of bicritical and polycritical points, where at least two or three second-order phase-transition lines intersect, respectively. The results are applied to the superconductivity phase diagram of ${\mathrm{UPt}}_3$.

• Received 27 November 1990

DOI:https://doi.org/10.1103/PhysRevB.43.2742