paper

The frustrated Heisenberg antiferromagnet on the checkerboard lattice: the -- model

arXiv:1202.2722 · doi:10.1103/PhysRevB.85.205122

Abstract

We study the ground-state (gs) phases of the spin-half anisotropic planar pyrochlore (or crossed chain) model using the coupled cluster method (CCM). The model is a frustrated antiferromagnetic (AFM) -- system on the checkerboard lattice, with nearest-neighbor exchange bonds and next-nearest-neighbor bonds . Using various AFM classical ground states as CCM model states we present results for their gs energy, average on-site magnetization, and susceptibilities to plaquette valence-bond crystal (PVBC) and crossed-dimer valence-bond crystal (CDVBC) ordering. We show that the state with Neel ordering is the gs phase for , but that none of the fourfold set of AFM states selected by quantum fluctuations at in a large- analysis (where is the spin quantum number) from the infinitely degenerate set of AFM states that form the gs phase for the classical version of the model (for ) survives the quantum fluctuations to form a stable magnetically-ordered gs phase for the spin-half case. The Neel state becomes susceptible to PVBC ordering at or very near to , and the fourfold AFM states become infinitely susceptible to PVBC ordering at . In turn, we find that these states become infinitely susceptible to CDVBC ordering for all values of above a certain critical value at or very near to . We thus find a Neel-ordered gs phase for , a PVBC-ordered phase for , and a CDVBC-ordered phase for . Both transitions are probably direct ones, although we cannot exclude very narrow coexistence regions confined to and respectively.

12 pages, 6 figures

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