The spectral weight of the Hubbard model through cluster perturbation theory

We calculate the spectral weight of the one- and two-dimensional Hubbard models, by performing exact diagonalizations of finite clusters and treating inter-cluster hopping with perturbation theory. Even with relatively modest clusters (e.g. 12 sites), the spectra thus obtained give an accurate description of the exact results. Thus, spin-charge separation (i.e. an extended spectral weight bounded by singularities) is clearly recognized in the one-dimensional Hubbard model, and so is extended spectral weight in the two-dimensional Hubbard model.Comment: 4 pages, 5 figure

One particle interchain hopping in coupled Hubbard chains

Interchain hopping in systems of coupled chains of correlated electrons is investigated by exact diagonalizations and Quantum-Monte-Carlo methods. For two weakly coupled Hubbard chains at commensurate densities (e.g. n=1/3) the splitting at the Fermi level between bonding and antibonding bands is strongly reduced (but not suppressed) by repulsive interactions extending to a few lattice spacings. The magnitude of this reduction is directly connected to the exponent $\alpha$ of the 1D Luttinger liquid. However, we show that the incoherent part of the single particle spectral function is much less affected by the interchain coupling. This suggests that incoherent interchain hopping could occur for intermediate $\alpha$ values.Comment: 4 pages, LaTeX 3.0, 7 PostScript figures in uuencoded for

One-Particle Spectral Properties of Mott-Hubbard Insulators

We use an exact holon and spinon Landau-liquid functional which describes the holon - spinon interactions at all scattering orders, to study correlation functions of integrable multicomponent many-particle problems showing both linear and non-linear energy bands. We consider specific cases when the dominant non-linear band terms are quadratic and apply our results to the evaluation of the 1D Hubbard model correlation functions beyond conformal-field theory.Comment: 10 Pages, Revte