1,276 research outputs found
Plasmons in strongly correlated systems: spectral weight transfer and renormalized dispersion
We study the charge-density dynamics within the two-dimensional extended
Hubbard model in the presence of long-range Coulomb interaction across the
metal-insulator transition point. To take into account strong correlations we
start from self-consistent extended dynamical mean-field theory and include
non-local dynamical vertex corrections through a ladder approximation to the
polarization operator. This is necessary to fulfill charge conservation and to
describe plasmons in the correlated state. The calculated plasmon spectra are
qualitatively different from those in the random-phase approximation: they
exhibit a spectral density transfer and a renormalized dispersion with enhanced
deviation from the canonical -behavior. Both features are reminiscent
of interaction induced changes found in single-electron spectra of strongly
correlated systems.Comment: 5 pages, 5 figures + appendix (3 pages, 1 figure
Conservation in two-particle self-consistent extensions of dynamical-mean-field-theory
Extensions of dynamical-mean-field-theory (DMFT) make use of quantum impurity
models as non-perturbative and exactly solvable reference systems which are
essential to treat the strong electronic correlations. Through the introduction
of retarded interactions on the impurity, these approximations can be made
two-particle self-consistent. This is of interest for the Hubbard model,
because it allows to suppress the antiferromagnetic phase transition in
two-dimensions in accordance with the Mermin-Wagner theorem, and to include the
effects of bosonic fluctuations. For a physically sound description of the
latter, the approximation should be conserving. In this paper we show that the
mutual requirements of two-particle self-consistency and conservation lead to
fundamental problems. For an approximation that is two-particle self-consistent
in the charge- and longitudinal spin channel, the double occupancy of the
lattice and the impurity are no longer consistent when computed from
single-particle properties. For the case of self-consistency in the charge- and
longitudinal as well as transversal spin channels, these requirements are even
mutually exclusive so that no conserving approximation can exist. We illustrate
these findings for a two-particle self-consistent and conserving DMFT
approximation.Comment: 17 pages, 9 figure
Self-consistent Dual Boson approach to single-particle and collective excitations in correlated systems
We propose an efficient dual boson scheme, which extends the DMFT paradigm to
collective excitations in correlated systems. The theory is fully
self-consistent both on the one- and on the two-particle level, thus describing
the formation of collective modes as well as the renormalization of electronic
and bosonic spectra on equal footing. The method employs an effective impurity
model comprising both fermionic and bosonic hybridization functions. Only
single- and two-electron Green's functions of the reference problem enter the
theory, due to the optimal choice of the self-consistency condition for the
effective bosonic bath. We show that the theory is naturally described by a
dual Luttinger-Ward functional and obeys the relevant conservation laws.Comment: 17 pages, 12 figure
Two-particle Fermi liquid parameters at the Mott transition: Vertex divergences, Landau parameters, and incoherent response in dynamical mean-field theory
We consider the interaction-driven Mott transition at zero temperature from the viewpoint of microscopic Fermi liquid theory. To this end, we derive an exact expression for the Landau parameters within the dynamical mean-field theory (DMFT) approximation to the single-band Hubbard model. At the Mott transition, the symmetric and the antisymmetric Landau parameters diverge. The vanishing compressibility at the Mott transition directly implies the divergence of the forward-scattering amplitude in the charge sector, which connects the proximity of the Mott phase to a tendency toward phase separation. We verify the expected behavior of the Landau parameters in a DMFT application to the Hubbard model on the triangular lattice at finite temperature. Exact conservation laws and the Ward identity are crucial to capture vertex divergences related to the Mott transition. We furthermore generalize Leggett's formula for the static susceptibility of the Fermi liquid to the static fermion-boson response function. In the charge sector, the limits of small transferred momentum and frequency of this response function commute at the Mott transition
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