27 research outputs found
The Out-of-Equilibrium Time-Dependent Gutzwiller Approximation
We review the recently proposed extension of the Gutzwiller approximation, M.
Schiro' and M. Fabrizio, Phys. Rev. Lett. 105, 076401 (2010), designed to
describe the out-of-equilibrium time-evolution of a Gutzwiller-type variational
wave function for correlated electrons. The method, which is strictly
variational in the limit of infinite lattice-coordination, is quite general and
flexible, and it is applicable to generic non-equilibrium conditions, even far
beyond the linear response regime. As an application, we discuss the quench
dynamics of a single-band Hubbard model at half-filling, where the method
predicts a dynamical phase transition above a critical quench that resembles
the sharp crossover observed by time-dependent dynamical mean field theory. We
next show that one can actually define in some cases a multi-configurational
wave function combination of a whole set of mutually orthogonal Gutzwiller wave
functions. The Hamiltonian projected in that subspace can be exactly evaluated
and is equivalent to a model of auxiliary spins coupled to non-interacting
electrons, closely related to the slave-spin theories for correlated electron
models. The Gutzwiller approximation turns out to be nothing but the mean-field
approximation applied to that spin-fermion model, which displays, for any
number of bands and integer fillings, a spontaneous symmetry breaking
that can be identified as the Mott insulator-to-metal transition.Comment: 25 pages. Proceedings of the Hvar 2011 Workshop on 'New materials for
thermoelectric applications: theory and experiment
Fermi-Surface Reconstruction in the Periodic Anderson Model
We study ground state properties of periodic Anderson model in a
two-dimensional square lattice with variational Monte Carlo method. It is shown
that there are two different types of quantum phase transition: a conventional
antiferromagnetic transition and a Fermi-surface reconstruction which
accompanies a change of topology of the Fermi surface. The former is induced by
a simple back-folding of the Fermi surface while the latter is induced by
localization of electrons. The mechanism of these transitions and the
relation to the recent experiments on Fermi surface are discussed in detail.Comment: 8 pages, 7 figures, submitted to Journal of the Physical Society of
Japa
Sum-rule corrections: a route to error cancellations in correlation matrix renormalisation theory
Efficient and accurate treatment of electron correlations with Correlation Matrix Renormalization theory
Uncovering the Origin of Divergence in the CsM(CrO4)2 (M = La, Pr, Nd, Sm, Eu; Am) Family through Examination of the Chemical Bonding in a Molecular Cluster and by Band Structure Analysis
A series
of f-block chromates, CsMÂ(CrO<sub>4</sub>)<sub>2</sub> (M = La, Pr,
Nd, Sm, Eu; Am), were prepared revealing notable differences
between the Am<sup>III</sup> derivatives and their lanthanide analogs.
While all compounds form similar layered structures, the americium
compound exhibits polymorphism and adopts both a structure isomorphous
with the early lanthanides as well as one that possesses lower symmetry.
Both polymorphs are dark red and possess band gaps that are smaller
than the Ln<sup>III</sup> compounds. In order to probe the origin
of these differences, the electronic structure of α-CsSmÂ(CrO<sub>4</sub>)<sub>2</sub>, α-CsEuÂ(CrO<sub>4</sub>)<sub>2</sub>,
and α-CsAmÂ(CrO<sub>4</sub>)<sub>2</sub> were studied using both
a molecular cluster approach featuring hybrid density functional theory
and QTAIM analysis and by the periodic LDA+GA and LDA+DMFT methods.
Notably, the covalent contributions to bonding by the f orbitals were
found to be more than twice as large in the Am<sup>III</sup> chromate
than in the Sm<sup>III</sup> and Eu<sup>III</sup> compounds, and even
larger in magnitude than the Am-5f spin–orbit splitting in
this system. Our analysis indicates also that the Am–O covalency
in α-CsAmÂ(CrO<sub>4</sub>)<sub>2</sub> is driven by the degeneracy
of the 5f and 2p orbitals, and not by orbital overlap