Fluctuations in the flat and collapsed phases of polymerized membranes

Fluctuations in polymerized membranes are explored via extensive molecular dynamics simulations of simplified 'tethered surface' models. The entropic rigidity associated with repulsive second-nearest-neighbor interactions leads to a flattening of ≪ phantom surfaces ≫. An attractive interaction in the presence of distant self-avoidance leads to a collapsed membrane with fractal dimension three at sufficiently low temperatures. When the attractive interaction is turned off, the surface returns to the flat phase found in earlier simulations. A study of density profiles and hexatic internal order allows a simple physical interpretation of results for the structure function of oriented membranes.