315 research outputs found
Theory of Core-Level Photoemission and the X-ray Edge Singularity Across the Mott Transition
The zero temperature core-level photoemission spectrum is studied across the
metal to Mott insulator transition using dynamical mean-field theory and
Wilson's numerical renormalization group. An asymmetric power-law divergence is
obtained in the metallic phase with an exponent alpha(U,Q)-1 which depends on
the strength of both the Hubbard interaction U and the core-hole potential Q.
For Q <~ U_c/2 alpha decreases with increasing U and vanishes at the transition
(U -> U_c) leading to a symmetric peak in the insulating phase. For Q >~ U_c/2,
alpha remains finite close to the transition, but the integrated intensity of
the power-law vanishes and there is no associated peak in the insulator. The
weight and position of the remaining peaks in the spectra can be understood
within a molecular orbital approach.Comment: 5 pages, 6 figure
On the nature of the Mott transition in multiorbital systems
We analyze the nature of Mott metal-insulator transition in multiorbital
systems using dynamical mean-field theory (DMFT). The auxiliary multiorbital
quantum impurity problem is solved using continuous time quantum Monte Carlo
(CTQMC) and the rotationally invariant slave-boson (RISB) mean field
approximation. We focus our analysis on the Kanamori Hamiltonian and find that
there are two markedly different regimes determined by the nature of the lowest
energy excitations of the atomic Hamiltonian. The RISB results at
suggest the following rule of thumb for the order of the transition at zero
temperature: a second order transition is to be expected if the lowest lying
excitations of the atomic Hamiltonian are charge excitations, while the
transition tends to be first order if the lowest lying excitations are in the
same charge sector as the atomic ground state. At finite temperatures the
transition is first order and its strength, as measured e.g. by the jump in the
quasiparticle weight at the transition, is stronger in the parameter regime
where the RISB method predicts a first order transition at zero temperature.
Interestingly, these results seem to apply to a wide variety of models and
parameter regimes.Comment: Accepted for publication in Physical Review
STM conductance of Kondo impurities on open and structured surfaces
We study the scanning tunneling microscopy response for magnetic atoms on
open and structured surfaces using Wilson's renormalization group. We observe
Fano resonances associated with Kondo resonances and interference effects. For
a magnetic atom in a quantum corral coupled to the confined surface states, and
experimentally relevant parameters, we observe a large confinement induced
effect not present in the experiments. These results suggest that the Kondo
screening is dominated by the bulk electrons rather than the surface ones.Comment: 6 pages, 6 figure
State-of-the-art techniques for calculating spectral functions in models for correlated materials
The dynamical mean field theory (DMFT) has become a standard technique for
the study of strongly correlated models and materials overcoming some of the
limitations of density functional approaches based on local approximations. An
important step in this method involves the calculation of response functions of
a multiorbital impurity problem which is related to the original model.
Recently there has been considerable progress in the development of techniques
based on the density matrix renormalization group (DMRG) and related matrix
product states (MPS) implying a substantial improvement to previous methods. In
this article we review some of the standard algorithms and compare them to the
newly developed techniques, showing examples for the particular case of the
half-filled two-band Hubbard model.Comment: 8 pages, 4 figures, to be published in EPL Perspective
Vibrational inelastic scattering effects in molecular electronics
We describe how to treat the interaction of travelling electrons with
localised vibrational modes in nanojunctions. We present a multichannel
scattering technique which can be applied to calculate the transport properties
for realistic systems, and show how it is related to other methods that are
useful in particular cases. We apply our technique to describe recent
experiments on the conductance through molecular junctions.Comment: LaTeX, 12 pages, 3 figure
Magnetic Structure of Hydrogen Induced Defects on Graphene
Using density functional theory (DFT), Hartree-Fock, exact diagonalization,
and numerical renormalization group methods we study the electronic structure
of diluted hydrogen atoms chemisorbed on graphene. A comparison between DFT and
Hartree-Fock calculations allows us to identify the main characteristics of the
magnetic structure of the defect. We use this information to formulate an
Anderson-Hubbard model that captures the main physical ingredients of the
system, while still allowing a rigorous treatment of the electronic
correlations. We find that the large hydrogen-carbon hybridization puts the
structure of the defect half-way between the one corresponding to an adatom
weakly coupled to pristine graphene and a carbon vacancy. The impurity's
magnetic moment leaks into the graphene layer where the electronic correlations
on the C atoms play an important role in stabilizing the magnetic solution.
Finally, we discuss the implications for the Kondo effect.Comment: 10 pages, 10 fig
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