Abstract
The defect-mediated phase transition in the fully frustrated XY model is discussed. A Migdal-Kadanoff position-space renormalisation group analysis (1976) is employed to investigate the critical behaviour of a similar model in the same universality class as the fully frustrated XY model. The resulting phase diagram shows that XY order cannot coexist with Ising disorder. This is in agreement with the recently suggested phase transition scenario in the fully frustrated XY model.