Pairing Correlations in Hot Nuclei

Abstract

The phase transition of pairing correlations is one of the interesting phenomena of hot nuclei and is always connected with broken symmetry. In this work, the pairing correlations in hot nuclei $^{162}$Dy are investigated in terms of the thermodynamical properties by covariant density functional theory. The thermodynamical quantities are evaluated by the canonical ensemble theory and the paring correlations are treated by a shell-model-like approach, in which the particle number is conserved exactly. An S-shaped heat capacity curve as a function of temperature has been obtained, which indicates a pairing transition from the superfluid to the normal state. The properties of hot nuclei are studied in terms of defined seniority component. It is found that the one-pair-broken ($s$= 2) states play crucial roles in the appearance of the S shape of the heat capacity curve. Meanwhile, we could predict that higher seniority sates may lead to higher term S shape of heat capacity at high temperature. Moreover, compared with the calculation results of finite temperature BCS, the pairing gap varies smoothly with the temperature due to the effect of the particle-number conservation, which indicates a gradual transition from the superfluid to the normal state.