Free Energy Functionals for Superfluid 3He
From the first suggestions in the early 1960’s of the possibility of pairing in 3He, until well after the discovery of the A and B phases in 1972, theoretical investigations of the properties of 3He with pairing took as a working assumption that this system would be well described by the simplest possible combination of BCS pairing theory and Landau’s Fermi liquid theory. The Fermi liquid theory provides an exact account of normal 3He just above Tc in terms of interacting quasi-particles, and corrections to BCS pairing theory for these quasi-particles were expected to be of order (kFξO)-1 ~ (Tc/TF) ~ 3 × 10-3. However, experiments on the A and B phases soon showed this assumption to be incorrect.1 In particular, the experiments imply that both new phases have odd-ℓ, spin-triplet pairing; that ℓ is the same in both phases; and that 3He-A is an equal-spin pairing state, while 3He-B is not. BCS pairing theory, on the other hand, predicts that the equilibrium state for triplet pairing is never an equal-spin pairing state.2 Furthermore, in simple BCS theories ΔC/CN, the ratio of the specific heat discontinuity at Tc to the specific heat in the normal phase just above Tc, is always ≤ 1.43, while experiments at melting pressure give ΔC/CN ≅ 2.0.
KeywordsFree Energy Vertex Function Melting Pressure Fermi Liquid Theory Exact Account
Unable to display preview. Download preview PDF.