Attractive and repulsive contributions of medium fluctuations to nuclear superfluidity.pdf

a r X i v : n u c l - t h / 0 5 0 2 0 7 7 v 1 2 3 F e b 2 0 0 5 Attractive and repulsive contributions of medium fluctuations to nuclear superfluidity G.Goria,b, F.Ramponia,b, F.Barrancoc, P.F. Bortignona,b, R.A. Brogliaa,b,d, G. Colo?a,b, E.Vigezzib a Dipartimento di Fisica, Universita? degli Studi di Milano, via Celoria 16, 20133 Milano, Italy. b INFN, Sezione di Milano, via Celoria 16, 20133 Milano, Italy. c Departamento de Fisica Aplicada III, Escuela Superior de Ingenieros, Camino de los Descubrimientos s/n, 41092 Sevilla, Spain. d The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen ?, Denmark. (Dated: February 9, 2008) Oscillations of mainly surface character (S = 0 modes) give rise, in atomic nuclei, to an attractive (induced) pairing interaction, while spin (S = 1) modes of mainly volume character generate a repulsive interaction, the net effect being an attraction which accounts for a sizeable fraction of the experimental pairing gap. Suppressing the particle-vibration coupling mediated by the proton degrees of freedom, i.e., mimicking neutron matter, the total surface plus spin-induced pairing interaction becomes repulsive. PACS numbers: 21.10.-k Properties of nuclei; nuclear energy levels; 21.30.Fe Forces in hadronic systems and effective interactions; 21.60.Ev Collective models; 21.60.Jz Hartree-Fock and random-phase approximations; 27.60.+j 90A149; A central issue in a quantitative description of super- conductors (metals, doped fullerides, etc.) as well as su- perfluid Fermi systems (3He, trapped gases of fermionic atoms, atomic nuclei, neutron stars, etc.) is related to the interaction acting between fermions and giving rise to Cooper pairs. The glue holding together the fermions of each Cooper pair, is the result of the bare interaction act- ing between fermions, strongly renormalized by medium polarization effects: Coulomb interaction plus plasmon and phonon exchange in metals [1], Van der Waals inter- action plu