Temperature-induced pair correlations in clusters and nuclei

Abstract

The pair correlations in mesoscopic systems such as nanometer-size superconducting clusters and nuclei are studied at a finite temperature for the canonical ensemble of fermions in model spaces with a fixed particle number: (i) a degenerate spherical shell (strong-coupling limit), (ii) an equidistantly spaced deformed shell (weak-coupling limit). It is shown that after the destruction of the pair correlations at $T=0$ by a strong magnetic field or rapid rotation, heating can bring them back. This phenomenon is a consequence of the fixed number of fermions in the canonical ensemble.