paper

The frustrated spin- -- isotropic model on the honeycomb lattice

arXiv:1403.2252 · doi:10.1103/PhysRevB.89.214413

Abstract

We study the zero-temperature ground-state (GS) phase diagram of a spin-half -- model on the honeycomb lattice with nearest-neighbor exchange coupling and frustrating next-nearest-neighbor exchange coupling , where both bonds are of the isotropic type, using the coupled cluster method. Results are presented for the GS energy per spin, magnetic order parameter, and staggered dimer valence-bond crystalline (SDVBC) susceptibility, for values of the frustration parameter in the range . In this range we find phases exhibiting, respectively, Néel planar [N(p)], Néel -aligned [N()], SDVBC, and Néel-II planar [N-II(p)] orderings which break the lattice rotational symmetry. The N(p) state, which is stable for the classical version of the model in the range , is found to form the GS phase out to a first quantum critical point at , beyond which the stable GS phase has N() order over the range . For values we find a strong competition to form the GS phase between states with N-II(p) and SDVBC forms of order. Our best estimate, however, is that the stable GS phase over the range is a mixed state with both SDVBC and N-II(p) forms of order; and for values is the N-II(p) state, which is stable at the classical level only at the highly degenerate point . Over the range we find no evidence for any of the spiral phases that are present classically for all values , nor for any quantum spin-liquid state.

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