On the layering transition of an SOS surface interacting with a wall. II. The Glauber dynamics

We continue our study of the statistical mechanics of a 2D surface above a fixed wall and attracted towards it by means of a very weak positive magnetic fieldh in the solid on solid (SOS) approximation, when the inverse temperature is very large. In particular we consider a Glauber dynamics for the above model and study the rate of approach to equilibrium in a large cube with arbitrary boundary conditions. Using the results proved in the first paper of this series we show that for allh(h _k+1 ^* ,h _k ^* ) ({h _k ^* } being the critical values of the magnetic field found in the previous paper) the gap in the spectrum of the generator of the dynamics is bounded away from zero uniformly in the size of the box and in the boundary conditions. On the contrary, forh=h _k ^* and free boundary conditions, we show that the gap in a cube of sideL is bounded from above and from below by a negative exponential ofL. Our results provide a strong indication that, contrary to what happens in two dimensions, for the three dimensional dynamical Ising model in a finite cube at low temperature and very small positive external field, with boundary conditions that are opposite to the field on one face of the cube and are absent (free) on the remaining faces, the rate of exponential convergence to equilibrium, which is positive in infinite volume, may go to zero exponentially fast in the side of the cube.Work partially supported by grant SC1-CT91-0695 of the Commission of European Communities.