Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 7: Cold Atomic Gases
TT 7.4: Vortrag
Montag, 7. März 2016, 11:00–11:15, H18
Bosonic Self-Energy Functional Theory with Symmetry Breaking — •Dario Hügel1, Philipp Werner2, Lode Pollet1, and Hugo U. R. Strand2 — 1Department of Physics, Arnold Sommerfeld Center for Theoretical Physics and Center for NanoScience, Ludwig-Maximilians-Universität München, Theresienstrasse 37, 80333 Munich, Germany — 2Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
We derive a non-perturbative variational self-energy functional for symmetry-broken bosonic systems from the corresponding Baym-Kadanoff functional. The local physics of the Bose-Hubbard model in three dimensions, as well as its thermodynamical properties in two dimensions, can be accurately reproduced by searching for the stationary points of such a functional with respect to just three scalar variational parameters: a symmetry-breaking field, and the normal and anomalous components of an imaginary-time independent hybridization function. We further show how bosonic dynamical mean-field theory follows naturally from the self-energy functional when extending the formalism to an imaginary-time-dependent hybridization function, while the mean-field approximation is obtained when neglecting the contributions of non-condensed bosons.
The simplicity of the method makes studying more complex lattice boson systems tractable. In particular, it can be generalized to systems with synthetic gauge fields and spin-orbit interactions, where path integral Monte Carlo methods fail due to the notorious sign problem.