RESTORATION OF ISOTROPY FOR SPIN MODELS

Using real-space renormalisation techniques we analyse the Ising model on a Sierpinski gasket with anisotropic microscopic couplings, and ob serve a restoration of isotropy on macroscopic scales. In particular, via use of a decimation procedure directly on the fractal lattice, we calculate explicitly the exponential anisotropy decay coefficients nea r the isotropic regime for both ferromagnetic and antiferromagnetic sy stems. The results suggest the universality of the phenomenon in latti ce field theories on fractals. (C) 1997 Published by Elsevier Science B.V.