Properties of the two-dimensional random-bond ±J Ising spin glass

We develop an exact gauge-invariant method for studying the two-dimensional +/-J spin glass. It is applied to the case of an arbitrary concentration of(1 - p) positive and p negative bonds and is thus a generalization of the more commonly studied p = 50% model. The ground-state properties are examined and in particular it is shown that the spin correlation exponent eta remains constant over the range p(c) < p < 50%. The value obtained is eta = 0.34 +/- 0.02. A wide range of-values for eta is quoted in the literature. We indicate possible reasons for the discrepancies and indicate that there are potential advantages in doing calculations at concentrations markedly lower than 50%.