Journal
PHYSICAL REVIEW B
Volume 85, Issue 21, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.85.214406
Keywords
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Funding
- German Research Foundation (DFG) [FOR 723, FOR 912]
- Emmy-Noether Program
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We apply a recently developed functional renormalization group (FRG) scheme for quantum spin systems to the spin-1/2 antiferromagnetic XXZ model on a two-dimensional square lattice. Based on an auxiliary fermion representation we derive flow equations which allow a resummation of the perturbation series in the spin-spin interactions. Spin susceptibilities are calculated for different values of the anisotropy parameter. The phase transition between planar and axial ordering at the isotropic point is reproduced correctly. The results for the critical scales from the FRG as quantitative measures for the ordering temperatures are in good agreement with the exact solution only in the Ising limit. In particular on the easy-plane side, the deviations from critical temperatures obtained with quantum Monte Carlo are rather large. Furthermore, at the isotropic point the Mermin-Wagner theorem is violated such that a description of the critical behavior and an extraction of scaling exponents is not possible. We discuss possible reasons for these discrepancies.
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