Length scales for wetting transitions: Beyond the continuum Landau approximation for the interfacial binding potential

We show that the length scale -1, which appears in the interfacial binding potential of the effective Hamiltonian description of wetting transitions, should be identified with the true or exponential range of the pair-correlation function of the bulk (wetting) phase, rather than the Ornstein-Zernike (second-moment) bulk correlation length b. Since -1>b, this implies that the parameter =kBT2/4, which determines the values of critical exponents for critical wetting in three dimensions, is significantly smaller than initial estimates of this quantity. For the simple-cubic Ising model (b)-11.46 for TTR, the roughening temperature, and depending on the magnitude of the interfacial stiffness , we conclude 0.5 is appropriate for such temperatures. We discuss the implications for recent Monte Carlo studies of critical wetting. © 1992 The American Physical Society.