Spin-12 heisenberg antiferromagnet on an anisotropic kagome lattice

We use the coupled-cluster method to study the zero-temperature properties of an extended two-dimensional Heisenberg antiferromagnet formed from spin-12 moments on an infinite spatially anisotropic kagome lattice of corner-sharing isosceles triangles, with nearest-neighbor bonds only. The bonds have exchange constants J₁>0 along two of the three lattice directions and J₂≡κJ₁>0 along the third. In the classical limit, the ground-state (GS) phase for κ<12 has collinear ferrimagnetic (Néel^′) order where the J₂-coupled chain spins are ferromagnetically ordered in one direction with the remaining spins aligned in the opposite direction, while for κ>12 there exists an infinite GS family of canted ferrimagnetic spin states, which are energetically degenerate. For the spin-12 case, we find that quantum analogs of both these classical states continue to exist as stable GS phases in some regions of the anisotropy parameter κ, namely, for 0<κ<κ_c1 for the Néel^′ state and for (at least part of) the region κ>κ_c2 for the canted phase. However, they are now separated by a paramagnetic phase without either sort of magnetic order in the region κ_c1<κ<κ_c2, which includes the isotropic kagome point κ=1 where the stable GS phase is now believed to be a topological (Z₂) spin liquid. Our best numerical estimates are κ_c1=0.515±0.015 and κ_c2= 1.82±0.03.