Fluctuations and Odd-Even Effects in Small Superfluid Systems

R. ROSSIGNOLI; N. CANOSA; P. RING

ANNALS OF PHYSICS (NEW YORK)

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: Amsterdam; Año: 1999 vol. 275 p. 1 - 26

0003-4916

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.