Low Temperature Behavior and Crossovers of the Square Lattice Quantum Heisenberg Antiferromagnet

Abstract
We present thermodynamic measurements of various physical observables of the two-dimensional S=1/2 isotropic quantum Heisenberg antiferromagnet on a square lattice, obtained by quantum Monte Carlo methods. The results are in excellent agreement with field-theoretical predictions. The issue of the existence of a crossover from quantum critical to renormalized classical regime is clarified.