Freiburg 1999 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 40: Theorie V
HK 40.5: Vortrag
Mittwoch, 24. März 1999, 16:30–16:45, A
Two- and four-particle condensates in nuclei and nuclear matter — •Arne Schnell1, Gerd Röpke1, and Peter Schuck2 — 1FB Physik, Universität Rostock, D-18051 Rostock — 2Institut des Sciences Nucléaire, 53, Avenue des Matyrs, F-38026 Grenoble Cedex, France
We investigate the formation of two-particle and four-particle condensates in nuclear matter and finite nuclei. Starting from an analysis of experimental nuclear binding energies, we find strong hints for the occurrence of proton-neutron pariring in symmetric (N=Z) nuclei. With increasing isospin asymmetry this kind of pairing is strongly reduced. Possible signals of a four-particle (α) condensate, as it is predicted by nuclear matter calculations [1] at low densities, will be discussed. Using the local density approxmation (LDA) estimates for the gain in binding energy due to pairing/quartetting are given and compared with experimental data.
The nucleon level density is calculated in symmetric nuclear matter from the two-particle spectral function using the ladder T matrix approximation. Close to the critical temperature of the superfluidity phase transition and at subnuclear densities we find a pseudo gap in the level density. This effect will be discussed by comparing our results with standard BCS calculations. It is found that the condensate contains strong correlations which are neglected by BCS theory. Similarities to precritical behavior of high-TC superconductors will be discussed.
[1] G. Röpke, A. Schnell, P. Schuck, Phys. Rev. Lett. 80, 3177 (1998).