Fluctuations and Odd-Even Effects in Small Superfluid Systems

摘要

Fluctuations and odd-even effects in small superfluid systems at finite temperature are investigated by means of the static path plus RPA approximation. A general derivation of this method is presented,which allows a straightforward implementation in statistical ensembles with fixed number parity (NP).A significant smoothing of the superconducting to normal transition is obtained in systems where the gap is comparable to the level spacing,as well as a decrease of pairing correlations in the odd case. Results are shown for a schematic model, where an excellent agreement with exact canonical results is obtained with the present method, and then for a heavy nucleus.Comparison with NP projected BCS and BCS+RPA results is made. An effective BCS+RPA approach which remains smooth in transitional regions is also derived.