Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: CE: Spin Systems and Itinerant Magnets

TT 22.3: Talk

Wednesday, March 24, 2010, 10:00–10:15, H21

An FRG approach for quantum antiferromagnets — •Johannes Reuther and Peter Wölfle — Institut für Theorie der Kondensierten Materie, Karlsruher Institut für Technologie, Germany

We consider spin-1/2 Heisenberg antiferromagnets on two dimensional lattices. In particular we study the melting of magnetic order as an effect of frustration. Examples for such models are the J₁-J₂-model or the Heisenberg model on a triangular or Kagome lattice. The last two lattices are examples for geometrically frustrated systems. We rewrite the spin operators in the Hamiltonians in terms of auxiliary fermions which enable us to perform diagrammatic approximations. For the auxiliary particle constraint an exact projection scheme proposed by Popov and Fedotov is available. In order to sum up diagrams in a controlled way we apply the Functional Renormalization Group (FRG) in conjunction with a cutoff procedure called Katanin truncation. Calculating the magnetic susceptibility and the spin-spin correlations we are able to distinguish between magnetically ordered and paramagnetic phases. We find phase diagrams in good agreement with numerical studies.