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Europhysics Letters (EPL)

Non-Fermi liquids in the two-band extended Hubbard model

J. L Smith, Qimiao Si A

Published Jan 15, 1999• 74 citations
Publisher

Abstract

We study the non-Fermi liquid behavior in a two-band extended Hubbard model. In the limit of infinite dimensions, where only local correlations are taken into account, this model in the mixed-valence regime is known to display a metallic non-Fermi liquid phase with spin-charge separation. Here we address the effect of intersite RKKY-like interactions using an extended dynamical mean-field approach. We find that the spin-charge separation survives the quantum fluctuations associated with the intersite density-density and spin-exchange interactions. We determine the spin, charge, and single-particle correlation functions in the non-Fermi liquid state.

DOI
10.1209/epl/i1999-00151-4

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We study the non-Fermi liquid behavior in a two-band extended Hubbard model. In the limit of infinite dimensions, where only local correlations are taken into account, this model in the mixed-valence regime is known to display a metallic non-Fermi liquid phase with spin-charge separation. Here we address the effect of intersite RKKY-like interactions using an extended dynamical mean-field approach. We find that the spin-charge separation survives the quantum fluctuations associated with the intersite density-density and spin-exchange interactions. We determine the spin, charge, and single-particle correlation functions in the non-Fermi liquid state.
We study the effects of intersite RKKY-like interactions in the mixed valence regime of a two-band extended Hubbard model. This model is known to display a metallic non-Fermi liquid state with spin-charge separation in the standard D=∞D=\inftyD=∞ limit (where interactions lead to purely on-site fluctuations only). Using an extended D=∞D=\inftyD=∞ approach, we find that the spin-charge separation survives the quantum fluctuations associated with arbitrary intersite density-density interactions and a finite range of intersite spin-exchange interactions. We determine the qualitative behavior of the spin, charge, and single-particle correlation functions. The implications of these results for the solution in finite spatial dimensions are discussed.
We study the competition between intersite and local correlations in a spinless two-band extended Hubbard model by taking an alternative limit of infinite dimensions. We find that the intersite density fluctuations suppress the charge Kondo energy scale and lead to a Fermi liquid to non-Fermi-liquid transition for repulsive on-site density-density interactions. In the absence of intersite interactions, this transition reduces to the known Kosterlitz-Thouless transition. We show that a new line of non-Fermi-liquid fixed points replace those of the zero intersite interaction problem.
We study an extended Hubbard model in the limit of infinite dimensions. The local correlation functions of this model are those of a generalized asymmetric Anderson model. The impurity model displays a Fermi liquid phase, a phase with neither the spin nor the charge of the impurity quenched, and an intermediate phase with the spin but not the charge of the impurity quenched. This analysis establishes the existence of metallic non-Fermi-liquid phases of the lattice model over a wide range of parameters and electron densities. The non-Fermi-liquid phases describe metals with incoherent spin and/or charge excitations and self-similar local correlation functions.
I summarize recent work on non-Fermi liquids within a certain generalized Anderson impurity model as well as in the large-dimensionality (D) limit of the two-band extended Hubbard model. The competition between local charge and spin fluctuations leads either to a Fermi liquid with renormalized quasiparticle excitations, or to non-Fermi liquids with spin - charge separation. These results provide new insights into the phenomenological similarities and differences between different correlated metals. While presenting these results, I outline a general strategy of local approach to non-Fermi liquids in correlated electron systems.
We study an extended Hubbard model in the limit of infinite dimensions and its zero-dimensional counterpart, a generalized asymmetric Anderson model. In the impurity model we find three kinds of mixed valence states: (a) the usual strong-coupling state in which a resonance forms at the Fermi level; (b) a weak-coupling state in which neither the impurity spin nor the impurity charge degrees of freedom are quenched; and (c) an intermediate-coupling state where the spin but not the charge degree of freedom is quenched. The corresponding phases of the extended Hubbard model in infinite dimensions are (a) a Fermi liquid; (b) a non-Fermi-liquid state with incoherent charge and spin excitations; and (c) a non-Fermi-liquid state with incoherent charge but coherent spin excitations. The non-Fermi-liquid phases are incoherent metallic states with vanishing quasiparticle residue, self-similar local correlation functions, and asymptotically decoupled charge and spin excitations. The non-Fermi-liquid phases occur for a wide range of parameters.