Critical amplitude ratios for critical wetting in three dimensions: Observation of nonclassical behavior in the Ising model

The surface layer susceptibility ${\mathrm{\chi }}_1$ is investigated for critical wetting transitions in three dimensions. Whereas mean-field treatments predict that ${\mathrm{\chi }}_1$ diverges symmetrically at the transition, a renormalization-group (RG) analysis predicts that the critical amplitude ratio R should be a rapidly increasing function of the parameter ω that determines the strength of interfacial fluctuations. Existing Monte Carlo data for the simple-cubic Ising model show pronounced asymmetry in ${\mathrm{\chi }}_1$ and yield a value for the ratio R that is significantly greater than the mean-field result (unity). The data are consistent with RG predictions, provided ω∼0.3 for the Ising model at the temperature of the simulation.