Wr. Czart et al., SUPERFLUID CHARACTERISTICS OF THE ATTRACTIVE HUBBARD-MODEL FOR VARIOUS LATTICE STRUCTURES, Physica. C, Superconductivity, 272(1-2), 1996, pp. 51-61
We study the basic thermodynamic and electromagnetic properties of the
superconductor described by the negative-U Hubbard model (gap paramet
er Delta, critical temperature T-c, London penetration depth lambda, t
hermodynamic critical field H-c and Ginzburg-Landau correlation length
xi(GL)) The calculations are performed for square (SQ, d = 2), simple
cubic (SC, d = 3) and face-centered cubic (FCC, d = 3) lattices. We a
nalyze the results as a function of electron density n and interaction
U using the Hartree-Fock approximation in the weak-to-intermediate U
case combined with the conclusions from the perturbation theory valid
in the strong coupling limit. From the equality: lambda/xi(GL) = 1/roo
t 2 we find the boundaries between local and nonlocal electronic behav
iour of the U < 0 Hubbard model in the U-n parameter space. Using the
calculated values of T-c and lambda we compare the ''universal plot''
of T-c/T-c(m) versus [lambda(0)/lambda(m)(0)](2) (where: T-c(m) denote
s maximum T-c as a function of n and lambda(m)(0) corresponds to T-c(m
)) with the recent experimental data for various families of nonconven
tional superconductors and conclude that the best agreement can be obt
ained for intermediate values of the local attraction.