Pairing reentrance in odd nuclei at finite temperature

Pairing correlations typically decrease as temperature increases, but in some nuclei, pairing is enhanced within a specific temperature range. This phenomenon, known as pairing reentrance, often occurs in nuclei with an odd number of protons and/or neutrons and is possibly due to the configurations of single-particle levels, especially those close to the Fermi energy. In this study, we examine various nuclear single-particle level configurations that can produce this effect. Our findings show that, although configurations with an odd number of nucleons cause the pairing reentrance, this effect may decrease or even disappear by decreasing the distance between levels located close to the one occupied by the odd nucleon. This reduction leads to an increase in the Pauli blocking effect, which is likely attributed to the participation of nucleons in the neighboring levels into the blocking effect, particularly when the distance between these levels and that occupied by the odd nucleon is very small. Our calculations for realistic calcium isotopes confirm the presence of this phenomenon.