Renormalization Group Seminar
and Condensed Matter Theory Seminar
May 24, 2005, 9:30 , Large Seminar Room of the ITP
Michael Potthoff
(Institut für Theoretische Physik und Astrophysik, Universität Würzburg)
Dynamical variational approach to strongly interacting fermions
Since the seminal work of Baym, Kadanoff, Luttinger und Ward it is well
known
that the grand potential of a system of interacting electrons can be
written as a
functional of the self-energy which is stationary at the exact
(physical) self-energy.
As the functional relation is given via the skeleton-diagram expansion,
this variational
principle has usually been considered to be of limited use. It can be
shown, however,
that an exact evaluation of the functional is possible on a restricted
domain. This is
a key observation which allows to construct systematic, non-perturbative
and
thermodynamically consistent approximations.
This talk presents the main idea, a general discussion of its
consequences, and
the relation to cluster extension of dynamical mean-field theory in
particular. The
formalism is used to construct an alternative variational cluster
approximation and
applied to study short- and long-range antiferromagnetic order in the
two-dimensional
Hubbard model.
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