CRITICAL EXPONENTS OF THE FULLY FRUSTRATED 2-DIMENSIONAL XY MODEL

We present a detailed study of the critical properties of the two-dime nsional (2D) XY model with maximal frustration in a square lattice. We use extensive Monte Carlo simulations to study the thermodynamics of the spin and chiral degrees of freedom, concentrating on their correla tion functions. The gauge-invariant spin-spin correlation functions ar e calculated close to the critical point for lattice sizes up to 240 X 240, the chiral correlation functions are studied on lattices up to 9 6 X 96. We find that the critical exponents of the spin-phase transiti on are nu = 0. 3069 and eta = 0.1915, which are to be compared with th e unfrustrated XY model exponents nu = 1/2 and eta = 0.25. We also fin d that the critical exponents of the chiral transition are nu(chi) = 0 .875, 2beta = 0.1936, 2gamma' = 1.82, and 2gamma' = 1.025, which are d ifferent from the expected 2D Ising critical exponents. The spin-phase transition occurs at T(U(1)) = 0.446, which is about 7% above the est imated chiral critical temperature T(Z2) = 0.4206. However, because of the size of the statistical errors, it is difficult to decide with ce rtainty whether the transitions occur at the same or at slightly diffe rent temperatures. Finally, the jump in the helicity modulus in the fu lly frustrated system is found to be about 23% below the unfrustrated universal value. The most important consequence of these results is th at the fully frustrated XY model appears to be in a novel universality class. Recent successful comparisons of some of these results with ex perimental data are also briefly discussed.