Quench dynamics of a superfluid Fermi gas

With an eye toward the interpretation of so-called "cosmological" experiments performed on the low-temperature phases of He3, in which regions of the superfluid are destroyed by local heating with neutron radiation, we have studied the behavior of a Fermi gas subjected to uniform variations of an attractive BCS interaction parameter λ. In He3, the quenches induced by the rapid cooling of the "hot spots" back through the transition may lead to the formation of vortex loops via the Kibble-Zurek mechanism. A consideration of the free energy available in the quenched region for the production of such vortices reveals that the Kibble-Zurek scaling law gives at best a lower bound on the defect spacing. Further, for quenches that fall far outside the Ginzburg-Landau regime, the dynamics on the pair subspace, as initiated by quantum fluctuations, tends irreversibly to a self-driven steady state with a gap Δ∞ = (e2 N (0) λ -1)-1 2. In weak coupling, this is only half the BCS gap, the extra energy being taken up by the residual collective motion of the pairs.