SURFACE MAGNETIZATION OF APERIODIC ISING SYSTEMS - A COMPARATIVE-STUDY OF THE BOND AND SITE PROBLEMS

We investigate the influence of aperiodic perturbations on the critica l behaviour at a second-order phase transition. The bond and site prob lems are compared for layered systems and aperiodic sequences generate d through substitution. In the bond problem, the interactions between the layers are distributed according to an aperiodic sequence whereas in the site problem, the layers themselves follow the sequence. A rele vance-irrelevance criterion introduced by Luck for the bond problem is extended to discuss the site problem. It involves a wandering exponen t for pairs, which can be larger than the one considered previously in the bond problem. The surface magnetization of the layered two-dimens ional Ising model is obtained, in the extreme anisotropic limit, for t he period-doubling and Thue-Morse sequences.