Quantum Phase Transition in a Heisenberg Antiferromagnet on a Square Lattice with Strong Plaquette Interactions
Abstract
We present numerical results for an S=1/2 Heisenberg antiferromagnet on a inhomogeneous square lattice with tunable interaction between spins belonging to different plaquettes. Employing Quantum Monte Carlo, we significantly improve on previous results for the the critical point separating singlet-disordered and N\'eel-ordered phases, and obtain an estimate for the critical exponent consistent with the three-dimensional classical Heisenberg universality class. Additionally, we show that a fairly accurate result for the critical point can be obtained from a Contractor Renormalization (CORE) expansion by applying a surprisingly simple analysis to the effective Hamiltonian.
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