CRITICALITY IN THE 2-DIMENSIONAL RANDOM-BOND ISING-MODEL

The two-dimensional (2D) random-bond Ising model has a novel multicrit ical point on the ferromagnetic to paramagnetic phase boundary. This r andom phase transition is one of the simplest examples of a 2D critica l point occurring at both finite temperatures and disorder strength. W e study the associated critical properties, by mapping the random 2D I sing model onto a network model. The model closely resembles network m odels of quantum Hall plateau transitions, but has different symmetrie s. Numerical transfer matrix calculations enable us to obtain estimate s for the critical exponents at the random Ising phase transition. The values are consistent with recent estimates obtained from high-temper ature series.