RELEVANT APERIODIC MODULATION IN THE 2D ISING-MODEL

We consider the surface critical behaviour of a semi-infinite two-dime nsional layered Ising model, where the coupling perpendicular to the s urface follow the aperiodic Rudin-Shapiro sequence. The model has unus ual critical properties: depending on the strength of the modulation, at the bulk critical point the surface magnetization is either discont inuous or vanishes with an essential singularity. The critical surface magnetization as well as the form of the essential singularity are ca lculated exactly.