  Atomic nuclei and nano-scale metallic grains are in the crossover regime of
pairing correlations between the bulk limit, where the
Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity is valid, and the
fluctuation-dominated regime, where BCS theory breaks down. In this
fluctuation-dominated regime, the pairing gap is comparable to or smaller than
the single-particle mean level spacing. We discuss thermal signatures of
pairing correlations in nuclei and ultra-small metallic grains that survive
despite the large fluctuations of the pairing field.
