Particle-number conservation in static-path approximation for thermal superfluid systems

TL;DR

This study applies particle-number projection to the static-path approximation to analyze heat capacity and pairing correlations in superfluid nuclei, revealing how particle-number conservation influences thermal properties.

Contribution

It introduces a particle-number projected static-path approximation (NPSPA) to better understand thermal effects in superfluid nuclei, extending previous SPA methods.

Findings

NPSPA enhances the S shape in heat capacity curves.

Particle-number projection aligns the model with pairing gap indicators.

Differences between SPA and NPSPA are nucleus-dependent.

Abstract

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.