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Edge effects in the two-dimensional spin-1/2 Heisenberg antiferromagnet

We use quantum Monte Carlo simulations to study effects of free edges in the two-dimensional spin-1/2 Heisenberg antiferromagnet. We find that the magnetic response of an edge is smaller than the bulk susceptibility. This counter-intuitive quantum effect can be traced to enhanced antiferromagnetic nearest-neighbor spin correlations, i.e., tendency to local singlet formation, at and close to the edge. These correlations form a comb-like pattern, which can be reproduced with a simple variational valence-bond state. We also study rough edges, and find that these instead significantly enhance the susceptibility, due to local sublattice imbalance impeding singlet formation.