A "hidden" zero temperature bicritical point in the 2D anisotropic Heisenberg model: Monte Carlo simulations and novel finite...

By considering the appropriate finite size effect, we explain the connection between the Monte Carlo simulations of the two dimensional anisotropic Heisenberg antiferromagnet in a field and the early renormalization group calculation for the bicritical $episolon$ dimensions. We found that the long length scale physics of the Monte Carlo simulations is indeed captured by the anisotropic nonlinear $sigma$ model. Our Monte Carlo data and analysis confirm the bicritical point in two-dimensions in Heisenberg-like and occurs at $T=0$, therefore the uncertainty in the phase diagram of this model is removed.