1,205 research outputs found
A novel FLEX supplemented QMC approach to the Hubbard model
This paper introduces a novel ansatz-based technique for solution of the
Hubbard model over two length scales. Short range correlations are treated
exactly using a dynamical cluster approximation QMC simulation, while
longer-length-scale physics requiring larger cluster sizes is incorporated
through the introduction of the fluctuation exchange (FLEX) approximation. The
properties of the resulting hybrid scheme are examined, and the description of
local moment formation is compared to exact results in 1D. The effects of
electron-electron coupling and electron doping on the shape of the
Fermi-surface are demonstrated in 2D. Causality is examined in both 1D and 2D.
We find that the scheme is successful if QMC clusters of are used
(with sufficiently high temperatures in 1D), however very small QMC clusters of
lead to acausal results
The Dynamical Cluster Approximation (DCA) versus the Cellular Dynamical Mean Field Theory (CDMFT) in strongly correlated electrons systems
We are commenting on the article Phys. Rev. {\bf B 65}, 155112 (2002) by G.
Biroli and G. Kotliar in which they make a comparison between two cluster
techniques, the {\it Cellular Dynamical Mean Field Theory} (CDMFT) and the {\it
Dynamical Cluster Approximation} (DCA). Based upon an incorrect implementation
of the DCA technique in their work, they conclude that the CDMFT is a faster
converging technique than the DCA. We present the correct DCA prescription for
the particular model Hamiltonian studied in their article and conclude that the
DCA, once implemented correctly, is a faster converging technique for the
quantities averaged over the cluster. We also refer to their latest response to
our comment where they argue that instead of averaging over the cluster, local
observables should be calculated in the bulk of the cluster which indeed makes
them converge much faster in the CDMFT than in the DCA. We however show that in
their original work, the authors themselves use the cluster averaged quantities
to draw their conclusions in favor of using the CDMFT over the DCA.Comment: Comment on Phys. Rev. B 65, 155112 (2002). 3 pages, 2 figure
Protracted Screening in the Periodic Anderson Model
The asymmetric infinite-dimensional periodic Anderson model is examined with
a quantum Monte Carlo simulation. For small conduction band filling, we find a
severe reduction in the Kondo scale, compared to the impurity value, as well as
protracted spin screening consistent with some recent controversial
photoemission experiments. The Kondo screening drives a ferromagnetic
transition when the conduction band is quarter-filled and both the RKKY and
superexchange favor antiferromagnetism. We also find RKKY-driven ferromagnetic
and antiferromagnetic transitions.Comment: 5 pages, LaTeX and 4 PS figure
The Bose-Hubbard model on a triangular lattice with diamond ring-exchange
Ring-exchange interactions have been proposed as a possible mechanism for a
Bose-liquid phase at zero temperature, a phase that is compressible with no
superfluidity. Using the Stochastic Green Function algorithm (SGF), we study
the effect of these interactions for bosons on a two-dimensional triangular
lattice. We show that the supersolid phase, that is known to exist in the
ground state for a wide range of densities, is rapidly destroyed as the
ring-exchange interactions are turned on. We establish the ground-state phase
diagram of the system, which is characterized by the absence of the expected
Bose-liquid phase.Comment: 6 pages, 10 figure
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