94 research outputs found
From Slater to Mott-Heisenberg physics: The antiferromagnetic phase of the Hubbard model
We study the optical conductivity of the one-band Hubbard model in the N\'eel
state at half filling at T=0 using the dynamical mean-field theory. For small
values of the Coulomb parameter clear signatures of a Slater insulator expected
from a weak-coupling theory are found, while the strongly correlated system can
be well described in terms of a Mott-Heisenberg picture. However, in contrast
to the paramagnet, we do not find any evidence for a transition between these
two limiting cases but rather a smooth crossover as a function of the Coulomb
interaction.Comment: 8 pages, 9 figure
Half-filled Hubbard Model on a Bethe lattice with next-nearest neighbor hopping
We study the interplay between N\'eel-antiferromagnetism and the paramagnetic
metal-insulator-transition (PMIT) on a Bethe lattice with nearest and
next-nearest eighbor hopping and . We concentrate in this paper on
the situation at half-filling. For the PMIT outgrows the
antiferromagnetic phase and shows a scenario similar to VO. In this
parameter regime we also observe a novel magnetic phase.Comment: 8 pages, 10 figure
A Numerical Renormalization Group approach to Green's Functions for Quantum Impurity Models
We present a novel technique for the calculation of dynamical correlation
functions of quantum impurity systems in equilibrium with Wilson's numerical
renormalization group. Our formulation is based on a complete basis set of the
Wilson chain. In contrast to all previous methods, it does not suffer from
overcounting of excitation. By construction, it always fulfills sum rules for
spectral functions. Furthermore, it accurately reproduces local thermodynamic
expectation values, such as occupancy and magnetization, obtained directly from
the numerical renormalization group calculations.Comment: 13 pages, 7 figur
Van Hove singularities in the paramagnetic phase of the Hubbard model: a DMFT study
Using the dynamical mean-field theory (DMFT) we study the paramagnetic phase
of the Hubbard model with the density of states (DOS) corresponding to the
three-dimensional cubic lattice and the two-dimensional square lattice, as well
as a DOS with inverse square root singularity. We show that the electron
correlations rapidly smooth out the square-root van Hove singularities (kinks)
in the spectral function for the 3D lattice and that the Mott metal-insulator
transition (MIT) as well as the magnetic-field-induced MIT differ only little
from the well-known results for the Bethe lattice. The consequences of the
logarithmic singularity in the DOS for the 2D lattice are more dramatic. At
half filling, the divergence pinned at the Fermi level is not washed out, only
its integrated weight decreases as the interaction is increased. While the Mott
transition is still of the usual kind, the magnetic-field-induced MIT falls
into a different universality class as there is no field-induced localization
of quasiparticles. In the case of a power-law singularity in the DOS at the
Fermi level, the power-law singularity persists in the presence of interaction,
albeit with a different exponent, and the effective impurity model in the DMFT
turns out to be a pseudo-gap Anderson impurity model with a hybridization
function which vanishes at the Fermi level. The system is then a generalized
Fermi liquid. At finite doping, regular Fermi liquid behavior is recovered.Comment: 7 pages, 9 figure
- …