Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 33: Low-Dimensional Systems: Other Materials

TT 33.4: Talk

Tuesday, March 17, 2015, 10:15–10:30, H 3010

Low-energy effective interactions beyond cRPA by the functional renormalization group — •Michael Kinza and Carsten Honerkamp — Instititut für theoretische Festkörperphysik, RWTH Aachen University

In the derivation of low-energy effective models for solids targeting the bands near the Fermi level, the constrained random phase approximation (cRPA) has become an appreciated tool to compute the effective interactions. Here we present applications of a constrained functional renormalization group (cfRG) scheme to two simple multi-band systems and compare the resulting effective interactions to the cRPA. The employed wick-ordered fRG scheme generalizes the cRPA approach by including all interaction channels in an unbiased way. First we consider a multiband model for graphene, where we integrate out the σ-bands to get an effective theory for π-bands. It turns out that terms beyond cRPA are strongly suppressed by xy-plane reflection-symmetry of the bands and that in our model, the cRPA stays qualitatively correct even if one breaks this symmetry slightly. The second example is a model for a Cu-O-chain, where we consider an effective theory for the Cu 3d-orbital. Here the fRG data points to relevant corrections compared to the cRPA results.