Abstract
Recent numerical results [Gonzalez et al., Phys. Rev. Lett. 122, 017201 (2019); Shimada et al., J. Phys. Conf. Ser. 969, 012126 (2018)] point to the existence of a partial-disorder ground state for a spin-1/2 antiferromagnet on the stuffed honeycomb lattice, with 2/3 of the local moments ordering in an antiferromagnetic Néel pattern, while the remaining 1/3 of the sites display short-range correlations only, akin to a quantum spin liquid. We derive an effective model for this disordered subsystem, by integrating out fluctuations of the ordered local moments, which yield couplings in a formal expansion, with being the spin amplitude. The result is an effective triangular-lattice XXZ model, with planar ferromagnetic order for large and a stripe-ordered Ising ground state for small , the latter being the result of frustrated Ising interactions. Within the semiclassical analysis, the transition point between the two orders is located at , being very close to the relevant case . Near quantum fluctuations tend to destabilize magnetic order. We conjecture that this applies to , thus explaining the observed partial-disorder state.
- Received 30 December 2018
DOI:https://doi.org/10.1103/PhysRevB.99.155156
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