  Zn-Paratacamite is a rare spin 1/2 antiferromagnetic insulator with an ideal
kagome lattice structure in part of its phase diagram. As a function of Zn
doping, this material undergoes a structural distortion which relieves the
frustration and introduces magnetic order in the ground state, though the
precise nature of the order is not clear at this point. In this paper, we
present strong evidence for Neel ordering in the strongly distorted phase of
Zn-Paratacamite through the application of quantum Monte-Carlo techniques.
These numerical results support a recent Schwinger-boson mean field theory of
Zn-Paratacamite. For weak distortion, close to the ideal kagome limit, our
results indicate a regime with no Neel order but with a broken glide-plane
symmetry. For this model the glide-plane symmetry is broken by any valence bond
crystal. Hence, our results lend support to recent proposals of a valence bond
crystal ground state for the undistorted lattice. The phase transition between
the two phases could be in the deconfined universality class if it is not a
first order transition.
