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arXiv:cond-mat/9706201

Theory of the Marginal Fermi Liquid Spectrum in the Local Treatment of the Large-U Falicov-Kimball Model

M. S. Laad

Published Jun 19, 1997• 0 citations
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Abstract

The Marginal Fermi Liquid (MFL) hypothesis proposed by Varma et al is derived from a consistent treatment of local spinfluctuations in the Falicov-Kimball model (FKM). Within an infinite-dimensional mean-field approach, a marginal Fermi liquid susceptibility and single-particle self-energy are obtained near half-filling, and a Fermi liquid phase is recovered sufficiently away from half-filling, in agreement with indications from experiments which probe the normal state of the cuprates as a function of doping

DOI
10.48550/arxiv.cond-mat/9706201

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The Marginal Fermi Liquid (MFL) hypothesis proposed by Varma et al is derived from a consistent treatment of local spinfluctuations in the Falicov-Kimball model (FKM). Within an infinite-dimensional mean-field approach, a marginal Fermi liquid susceptibility and single-particle self-energy are obtained near half-filling, and a Fermi liquid phase is recovered sufficiently away from half-filling, in agreement with indications from experiments which probe the normal state of the cuprates as a function of doping
The diagrammatic formulation of the single-site approximation to the Hubbard model immediately yields the exact solution to the Falikov-Kimball model in infinite dimensions. By an extension of the alloy analogy, we then derive a two-fluid model, dividing self-consistently the electron system among itinerating and relatively localized particles. Our theory coincides with the CPA only the at half-filling and u=∞. We start by studying the mean field approximation to our theory and identify a phase boundary in the particle density-interaction strength (n−u) plane at which the Fermi liquid model breaks down. Then the effect of fluctuations in the Fermi liquid regime is considered and, finally, we construct, at half-filling, a model which interpolates between the Fermi liquid and the Mott insulating phases.
We find marginal-Fermi-liquid- (MFL) like behavior in the Hubbard model on a square lattice for a range of hole doping and on-site interaction parameter U. Thereby we use a self-consistent projection operator method. It enables us to compute the momentum and frequency dependence of the single-particle excitations with high resolution. The Fermi surface is found to be holelike in the underdoped regime and electronlike in the overdoped regime. Our calculations concern normal state properties of the system. When a comparison is possible, we find consistency with finite temperature quantum Monte Carlo results. We also find a discontinuous change with doping concentration from a MFL to a Fermi-liquid behavior resulting from a collapse of the lower Hubbard band. This renders Luttinger's theorem inapplicable in the underdoped regime.
Two-dimensional spinless Falicov-Kimball model (FKM) with correlated hopping is studied perturbatively in the limit of large on-site Coulomb interaction U. In the half filled case (i.e., ${\ensuremath{\rho}}_{i}+{\ensuremath{\rho}}_{e}=1,$ where ${\ensuremath{\rho}}_{i},{\ensuremath{\rho}}_{e}$ are densities of ions and electrons, respectively) the effective Hamiltonian in spin variables is derived up to terms proportional to ${U}^{\ensuremath{-}3}.$ Unlike the simplest FKM case, it contains odd parity terms (resulting from the correlated hopping) in addition to even parity ones. The ground-state phase diagram of the effective Hamiltonian is examined in the (a/t,h)(a/t,h)(a/t,h) plane, where a/ta/ta/t is a parameter characterizing strength of the correlated hopping and h is a difference of chemical potentials of two sorts of particles present in the system. It appears to be asymmetric with respect to the change $\stackrel{\ensuremath{\rightarrow}}{h}\ensuremath{-}h$ and an additional ordered phase is found for a certain interval of a/t.a/t.a/t.
The Hubbard model (HM) and the Falicov-Kimball model (FKM), which are two standard models of strongly correlated electrons, provide an interesting benchmark for the physics of locally correlated systems. We study the intermediate model, mass-imbalanced Hubbard model at half-filling on a 2D square lattice which connects continuously the HM to the FKM.We employ dynamical mean field theory (DMFT) and dynamical cluster approximation (DCA) using continuous-time auxiliary field method (CT-AUX) as self-consistent impurity solver to study the single particle spectral function and self-energy allowing us to map-out the phase diagram of the system. Solutions to the mass-imbalanced model cannot enforce paramagnetic self-consistency and therefore at low temperature result in paramagnetic (PM) to antiferromagnetic (AFM) transition. In addition, in the PM state and at finite temperature, we observed a spin dependent crossover from Fermi liquid (FL) regime to non-Fermi liquid (nFL) regime in which the FL regime is destroyed, monotonically, induced not only by the interaction but also by the mass imbalance. We present the results for small cluster DCA and explore its dependency on cluster size as well.
We reexamine the Brandt-Mielsch solution of the Falicov-Kimball model in infinite dimensions, to elucidate the mechanism for the breakdown of Fermi-liquid theory in this model. We find that this breakdown is due to the pinning of the chemical potential at the localized particle level. When this pinning does not occur, Fermi-liquid theory is restored. Using a Lorentzian density of states, we obtain analytic expressions for spectral densities and local response functions. These expressions give new insights into the formation of upper and lower Hubbard bands, the metal-insulator transition, the softening of the collective modes, and the infrared singularities of this model.
The Hubbard model is investigated starting from both the small and large U limits. This allows one to derive an interpolation formula for the double occupancy at half-filling for dimensionalities d = 1, 2, 3. It shows a smooth behavior as a function of U and tends to zero only for U → ∞. A quantity that probes more sensitively the nature of the ground state is the momentum distribution function n(k). At half filling n(k) is smooth at k F both for d = 1 and d = 2, at least for not too small values of U. In one dimension for all other band fillings the slope of n(k) has a power-law singularity at k F with an exponent α increasing steadily from zero at U = 0 to 1/8 for U → ∞; the system is a "marginal Fermi liquid". A similar behavior may occur close to half-filling for d = 2, but for small densities one expects the usual step function of a normal Fermi liquid.