DISORDER-INDUCED PHASE IN THE RANDOM BOND ISING-MODEL ON THE SQUARE LATTICE

The random bond Ising model in two dimensions is considered in terms of a random matrix representation. A generalization of this approach enables us to study an N --> infinity limit and the corresponding 1/N expansion. With g as the strength of the random bond fluctuations, the critical temperature T(c) of the pure system is split into two critical temperatures T +/- = T(c)(1 +/- c0 exp [-c1/g]) with a new phase for T- < T < T+. The specific heat, for instance, grows logarithmically (or double logarithmically in a crossover region near T +/-) with /1 - T/T(c)/ up to a bound of the order 1/g.