7,234 research outputs found
Spectral functions for single- and multi-Impurity models using DMRG
This article focuses on the calculation of spectral functions for single- and
multi-impurity models using the density matrix renormalization group (DMRG). To
calculate spectral functions from DMRG, the correction vector method is
presently the most widely used approach. One, however, always obtains
Lorentzian convoluted spectral functions, which in applications like the
dynamical mean-field theory can lead to wrong results. In order to overcome
this restriction we show how to use the Lehmann formula to calculate a peak
spectrum for the spectral function. We show that this peak spectrum is a very
good approximation to a deconvolution of the correction vector spectral
function. Calculating this deconvoluted spectrum directly from the DMRG basis
set and operators is the most natural approach, because it uses only
information from the system itself. Having calculated this excitation spectrum,
one can use an arbitrary broadening to obtain a smooth spectral function, or
directly analyze the excitations. As a nontrivial test we apply this method to
obtain spectral functions for a model of three coupled Anderson impurities.
Although, we are focusing in this article on impurity models, the proposed
method for calculating the peak spectrum can be easily adapted to usual lattice
models.Comment: 11 pages, 14 figure
Large and Small Fermi-Surface Spin Density Waves in the Kondo Lattice Model
We demonstrate the existence of metallic spin density waves (SDWs) in the
Kondo lattice model on a square lattice for a wide range of parameters by means
of real space dynamical mean field theory. In these SDWs, the spin polarization
as well as the charge density depend on the lattice site and are modulated
along one direction of the square lattice. We show that within this phase of
metallic SDWs the Fermi surface changes from small to large, when the coupling
strength is increased. Furthermore, the transition between the large
Fermi-surface SDW phase and the paramagnetic phase is of second order, while
the transition between the small Fermi-surface SDW phase and the paramagnetic
phase is of first order. A local quantum critical point is thus avoided in our
calculations by undergoing a first order phase transition
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
Magnetism in f electron superlattices
We analyze antiferromagnetism in electron superlattices. We show that the
competition between the Kondo effect and the RKKY interaction in electron
materials is modified by the superlattice structure. Thus, the quantum critical
point which separates the magnetic phase and the Fermi liquid phase depends on
the structure of the electron superlattice. The competition between the
Kondo effect and the RKKY interaction is also reflected in the magnetic
interlayer coupling between different electron layers. We demonstrate that
in the case of weak Kondo effect the magnetic interlayer coupling behaves
similar to other magnetic heterostructures without Kondo effect. However, close
to the quantum phase transition, the dependence of the interlayer coupling on
the distance between the electron layers is modified by the Kondo effect.
Another remarkable effect, which is characteristic for electron
superlattice, is that the magnetic interlayer coupling does vanish stepwise
depending on the distance between different electron layers. As a
consequence, the quantum critical point depends also stepwise on this distance
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