Symmetry breaking field in UPt${_3}$ and connection to superfluid ${^3}$He

The multiple superconducting phases of UPt${_3}$ in its temperature-field phase diagram are a strong indication of its unconventional order parameter. It is generally accepted that such a complex phase diagram with 3 different vortex phases are nearly degenerate, and would be so, except for the presence of a symmetry breaking field attributed to antiferromagnetism which appears at a temperature an order of magnitude higher than the superconducting transition.[1] I propose an alternative mechanism where the symmetry breaking field can be, in large part, ascribed to anisotropic electronic scattering from stacking faults. The success of the theory[2] in accounting for stabilization of anisotropic phases of superfluid ${^3}$He in globally anisotropic aerogel[3] suggests a similar consequence from anisotropic quasiparticle scattering in UPt${_3}$. Specific heat measurements indicate that the temperature window of the more anisotropic A-phase, a direct measure of the strength of the symmetry breaking field, decreases systematically with fewer stacking faults. [1] D.W. Hess {\it et al.}, J. Phys.: Condens. Matter {\bf 1}, 8135 (1989). [2] E.V. Thuneberg {\it et al.}, Phys. Rev. Lett. {\bf 80}, 2161 (1998). [3] J. Pollanen {\it et al.}, Nat. Phys. {\bf 8}, 317 (2012).