Evidence for Deconfined Quantum Criticality in a Two-Dimensional Heisenberg Model with Four-Spin Interactions

Using ground-state projector quantum Monte Carlo simulations in the valence-bond basis, it is demonstrated that nonfrustrating four-spin interactions can destroy the Néel order of the two-dimensional $S=1/2$ Heisenberg antiferromagnet and drive it into a valence-bond solid (VBS) phase. Results for spin and dimer correlations are consistent with a single continuous transition, and all data exhibit finite-size scaling with a single set of exponents, $z=1$, $\nu =0.78\pm 0.03$, and $\eta =0.26\pm 0.03$. The unusually large $\eta$ and an emergent $U(1)$ symmetry, detected using VBS order parameter histograms, provide strong evidence for a deconfined quantum critical point.