Generalized Spin Fluctuation Feedback in Heavy Fermion Superconductors

Experiments reveal that the superconductors UPt₃, PrOs₄Sb₁₂ and U_1-xTh_xBe₁₃ undergo two superconducting transitions in the absence of an applied magnetic field. The prevalence of these multiple transitions suggests a common underlying mechanism. A natural candidate theory which accounts for these two transitions is the existence of a small symmetry breaking field, however such a field has not been observed in PrOs₄Sb₁₂ or U_1-xTh_xBe₁₃ and has been called into question for UPt₃. Motivated by arguments originally developed for superfluid ³He we propose that a generalized spin fluctuation feedback effect is responsible for these two transitions. In this talk, we show that a phenomenological theory which couples spin fluctuations to superfluidity correctly predicts that a high temperature broken time-reversal superfluid ³He phase can emerge as a consequence. This phenomenological approach is then applied to these three superconductors revealing that this naturally leads to a high-temperature time-reversal invariant nematic superconducting phase, which can be followed by a second transition into a broken time-reversal symmetry phase, as observed.