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Dynamical mean field theory (DMFT) has been
successfully employed for studying strong
electronic correlations in models and for
electronic structure calculations of many
materials. However, DMFT is restricted to local
correlations and hence misses important aspects
of electronic correlations such as magnetic
fluctuations, d-wave superconductivity, and
quantum critical behavior. One way to overcome
this is through cluster extensions of DMFT which
are however restricted to short-range
correlations. For long-range correlations,
we develop a diagrammatic extension in which local
and nonlocal self-energy diagrams are constructed
from the local irreducible vertex. This dynamical
vertex approximation [1] includes the local
correlations of dynamical mean field theory
and long-range correlations beyond. It allows for
example to describe (para-)magnons and weak
localization effects in strongly correlated systems.
As first applications, we study the interplay between nonlocal antiferromagnetic correlations and the strong local correlations in the vicinity of a Mott-Hubbard transition as well as the emergence of a pseudogap in the two-dimensional Hubbard model. Briefly, I will also discuss our recent DMFT results [2] which show that kinks in the electronic dispersion naturally arise in purely electronic models if correlations are strong. [1] A. Toschi, A. A. Katanin, and K. Held, cond-mat/0603100 also see H. Kusunose, cond-mat/0602451 C. Slezak, M. Jarrell, Th. Maier, and J. Deisz, cond-mat/0603421. [2] K. Byczuk et al., cond-mat/0609594. |
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