Spontaneous breaking of layer symmetry in an Ising film and universality

Within the correlation length equality approach, introduced in previous papers, a spontaneous symmetry breaking phenomenon among the identical planes of a two-layer ferromagnetic Ising film is growing, according to which the divergence of the correlation length at the critical point is essentially due to a single plane developing strong correlations, the other plane acting as a “spectator”, which profits by these correlations. The phenomenon is responsible for the fact that the thermal critical exponent v does not depend on the coupling between the two planes and coincides with its value in the 2D Ising model.