CHIRAL-CORRELATION AND SPIN-CORRELATION FUNCTIONS IN A RANDOM-BOND XYLADDER

We analyze the role of discrete symmetry in a one-dimensional randomly frustrated XY model on a ladder lattice with +/-J bonds. In the Villa in formulation discrete-valued chiralities, associated with the plaque ttes of the lattice, are decoupled from the continuous spin-wave varia bles. Within a low-temperature (T) approximation, we show that the chi ralities and the XY spins have the same zero-T correlation-length expo nent, which we determine exactly. We also show how this exponent follo ws from antiperiodic and reflecting boundary conditions imposed on a f inite system at T = 0. A contrast appears between the ladder and a two -dimensional picture recently proposed.