CONDUCTIVITY IN A SYMMETRY-BROKEN PHASE - SPINLESS FERMIONS WITH 1 D CORRECTIONS/

The dynamic conductivity sigma(omega) of strongly correlated electrons in a symmetry-broken phase is investigated in the present work. The m odel considered consists of spinless fermions with repulsive interacti on on a simple cubic lattice. The investigated symmetry-broken phase i s the charge density wave (CDW) with wave vector Q=(pi, pi, pi)(dagger ) which occurs at half-filling. The calculations are based on the high dimensional approach, i.e., an expansion in the inverse dimension 1/d is used. The finite dimensionality is accounted for by the inclusion of linear terms in 1/d and the true finite dimensional DOS. Special ca re is paid to the setup of a conserving approximation in the sense of Baym/Kadanoff without inconsistencies. The resulting Bethe-Salpeter eq uation is solved for the dynamic conductivity in the nonsymmetry-broke n and in the symmetry-broken phase (AB-CDW). The de-conductivity is re duced drastically in the CDW. Yet it does not vanish in the limit T--> 0 due to a subtle cancellation of diverging mobility and vanishing DOS . In the dynamic conductivity sigma(omega) the energy gap induced by t he symmetry breaking is clearly discernible. In addition, the vertex c orrections of order 1/d lead to an excitonic resonance lying within th e gap.