Superfluid Phase Transitions and Effects of Thermal Pairing Fluctuations in Asymmetric Nuclear Matter.

ABSTRACT

We investigate superfluid phase transitions of asymmetric nuclear matter at finite temperature (T) and density (ρ) with a low proton fraction (Yp ≤ 0.2), which is relevant to the inner crust and outer core of neutron stars. A strong-coupling theory developed for two-component atomic Fermi gases is generalized to the four-component case, and is applied to the system of spin-1/2 neutrons and protons. The phase shifts of neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) interactions up to k = 2 fm-1 are described by multi-rank separable potentials. We show that the critical temperature [Formula see text] of the neutron superfluidity at Yp = 0 agrees well with Monte Carlo data at low densities and takes a maximum value [Formula see text]= 1.68 MeV at [Formula see text] with ρ0 = 0.17 fm-3. Also, the critical temperature [Formula see text] of the proton superconductivity for Yp ≤ 0.2 is substantially suppressed at low densities due to np-pairing fluctuations, and starts to dominate over [Formula see text] only above [Formula see text](0.77) for Yp = 0.1(0.2), and (iii) the deuteron condensation temperature [Formula see text] is suppressed at Yp ≤ 0.2 due to a large mismatch of the two Fermi surfaces.