The quasiparticle weight of the two-dimensional Hubbard model in thet-matrix approximation is discussed in comparison with a recent report by Yokoyama and Fukuyama (J. Phys. Soc. Jpn. 66 (1997), 529) where the breakdown of the quasiparticle description of the Fermi liquid was concluded.
Using the finite-size scaling of results obtained by exact diagonalization, we study the low-density limit of the one-dimensional Hubbard model. Calculating the quasiparticle weight, we demonstrate that for a given particle number N and system size L, there always exists a crossover point Uc separating the Fermi-liquid (UUc) and non-Fermi-liquid (U>Uc) regimes (U is the Hubbard repulsion). We find that for a fixed N, Uc is inversely proportional to L, keeping UcL/t constant (with t as the hopping integral), as L is large enough. It follows that in the low-density (in fact vanishing density) limit L\ensuremath{\rightarrow}\ensuremath{\infty}, Uc\ensuremath{\rightarrow}0, so the system is always in the non-Fermi-liquid regime as long as U>0. We show that our numerical results are consistent with the Bethe-ansatz solution.
We examine the validity of Fermi-liquid theory in the low-density two-dimensional Hubbard model. From the ground-state energy we obtain the quasiparticle energy and the Landau interaction function. Then we prove that the quasiparticle-interaction function is finite and that the quasiparticle residue is nonzero for repulsive interactions. We also find, as a function of the excitation energy \ensuremath{\epsilon}, that the quasiparticle lifetime \ensuremath{\sim}1/${\mathrm{\ensuremath{\epsilon}}}^{2}$ln\ensuremath{\epsilon}. Hence, we conclude that Fermi-liquid theory holds in our model.
For pt.I see Physics B, vol.163, p.527 (1990). An exact diagrammatic analysis of the electron self-energy in the Hubbard and related models is given within the local approximation. Contact is made with recent work for dimension d= infinity where the local approximation becomes exact. It is shown that the approximate method of paper I of the series may be fitted into the new framework and yields sensible results for the Anderson impurity model. This lends weight to the prediction of I that for paramagnetic solutions of the Hubbard model Fermi liquid behaviour breaks down in a whole region of the T=0 phase diagram, not just for a half-filled band where the Mott transition occurs.
It is shown that the energy (ε) and momentum (k) dependences of the electron self-energy function $ Σ(k, \varepsilon + i0) \equiv Σ^{R}(k, \varepsilon) $ are, $ {\rm Im} Σ^{R} (k, \varepsilon) = -a\varepsilon^{2}|\varepsilon - ξ_{k}|^{- γ(k)} $ where a is some constant, ξk=ε(k)−μ,ε(k) being the band energy, and the critical exponent $ γ(k) $, which depends on the curvature of the Fermi surface at $ k $, satisfies, $ 0 \leq γ(k) \leq 1 $. This leads to a new type of electron liquid, which is the Fermi liquid in the limit of $ \varepsilon, ξ_{k} \rightarrow 0 $ but for $ ξ_{k} \neq 0 $ has a split one-particle spectra as in the Tomonaga-Luttinger liquid.