Numerical Transfer-Matrix Study of Metastability in the d=2 Ising Model

We apply a generalized numerical transfer-matrix method to the 2-d Ising ferro- magnet in a nonzero field to obtain complex constrained free energies. Below $T_c$ certain eigenstates of the transfer matrix are identified as representing a metastable phase. The imaginary parts of the metastable constrained free energies are found to agree with a field-theoretic droplet model for a wide range of fields, allowing us to numerically estimate the average free-energy cost of a critical cluster. We find excellent agreement with the equilibrium cluster free energy obtained by a Wulff construction with the exact, aniso- tropic zero-field surface tension, and we present strong evidence for Gold- stone modes on the critical cluster surface. Our results are also fully con- sistent with average metastable lifetimes from previous Monte-Carlo simula- tions. The study indicates that our constrained-transfer-matrix technique pro- vides a nonperturbative numerical method to obtain an analytic continuation of the free energy around the essential singularity at the first-order transition.