Abstract
The ground state phase of a spin- antiferromagnetic Heisenberg model on a square lattice around the maximally frustrated regime has been debated for decades. Here we study this model using the cluster update algorithm for tensor-product states (TPSs). The ground state energies at finite sizes and in the thermodynamic limit (with finite size scaling) are in good agreement with exact diagonalization study. Through finite size scaling of the spin correlation function, we find the critical point and critical exponents . In the range of we find a paramagnetic ground state with an exponentially decaying spin-spin correlation. Up to a system size, we observe power law decaying dimer-dimer and plaquette-plaquette correlations with an anomalous plaquette scaling exponent and an anomalous columnar scaling exponent at . These results are consistent with a potential gapless spin-liquid phase. However, since the spin liquid is unstable due to the instanton effect, a valence bond solid order with very small amplitude might develop in the thermodynamic limit. Thus, our numerical results strongly indicate a deconfined quantum critical point at . Remarkably, all the observed critical exponents are consistent with the model.
- Received 24 May 2016
DOI:https://doi.org/10.1103/PhysRevB.94.075143
©2016 American Physical Society