Critical behavior of pure and dilutedXYmodels with uniform frustrations

Abstract

A renormalization-group approach is used to investigate phase transitions in fully frustrated XY models on a square and a triangular lattice. The existence of long-range order associated with the discrete symmetry of the system is demonstrated. It is argued that there exists one transition which is a combination of a Kosterlitz-Thouless–like one for spins and an Ising-like one for chirality. In particular a nonuniversal jump in the helicity modulus is predicted. Dilute randomness is also considered and shown to be irrelevant to the critical behavior.