  By applying particle-number projection to the static-path approximation
(SPA), the heat capacity and the breakdown of pairing correlations are
investigated in the thermally excited, superfluid systems 172Yb, 94Mo, and
56Fe. For the heavy nucleus 172Yb, the heat capacities in both the SPA and the
number-projected SPA (NPSPA) exhibit an S shape; the difference between the SPA
and NPSPA heat-capacity curves is not very large and the particle-number
projection thereby enhances the S shape already seen in the SPA. The
temperature at which the S-shape of heat capacity curve occurs parallels the
temperature of the breakdown of pairing correlations as indicated by the
effective pairing gap. However, for the comparatively lighter nuclei 94Mo and
56Fe, the SPA does not produce an S-shaped heat capacity on its own; only after
particle-number projection the S shape appears in the heat-capacity curve. For
94Mo, we compare the NPSPA result with thermal odd-even mass differences, which
are regarded as a direct measure of the pairing gap.
