Johannes Reuther, Uni-Karlsruhe
We apply the functional renormalization group (FRG) method to describe groundstate properties of frustrated spin-1/2 systems on two-dimensional lattices. In order to be able to use this technique, we rewrite the spin operators in terms of pseudo fermions. The resulting fermionic model is then treated via diagrammatic perturbation theory in the couplings. In that context, the FRG manages to sum up diagrammatic contributions in various different interaction channels in infinite order. Calculating the magnetic spin susceptibility, we are able to determine the groundstate phase diagrams of the spin systems under consideration. Thereby, we focus on models such as the frustrated Heisenberg model on a honeycomb lattice which is characterized by a complex interplay between different magnetically ordered and disordered phases. Additionally, the Heisenberg-Kitaev model which has become known in the context of topological quantum computation allows us to investigate spin-liquid behavior. We calculate the frustration parameter of this spin system in order to make contact to ongoing experiments.