FINITE-SIZE-SCALING ANALYSIS OF EXACT GROUND-STATES FOR + -J SPIN-GLASS MODELS IN 2 DIMENSIONS/

With the help of exact ground states obtained by a polynomial algorith m we compute the domain wall energy Delta at zero temperature for the bond-random and the site-random Ising spin glass model in two dimensio ns. We find that in both models the stability of the ferromagnetic and the spin glass order ceases to exist at a unique concentration p(c) f or the ferromagnetic bonds. In the vicinity of this critical point, th e size and concentration dependence of the first and second moment of the domain mall energy are, for both models, described by a common fin ite-size scaling form. Moreover, below this concentration the stiffnes s exponent turns out to be slightly negative, theta(S) = -0.056(6), in dicating the absence of any intermediate spin glass phase at non-zero temperature.