Multicritical Nishimori point in the phase diagram of the +/-J Ising model on a square lattice.

We investigate the critical behavior of the random-bond +/-J Ising model on a square lattice at the multicritical Nishimori point in the T-p phase diagram, where T is the temperature and p is the disorder parameter ( p=1 corresponds to the pure Ising model). We perform a finite-size scaling analysis of high-statistics Monte Carlo simulations along the Nishimori line defined by 2p-1=tanh(1/T) , along which the multicritical point lies. The multicritical Nishimori point is located at p;{ *}=0.890 81(7) , T;{ *}=0.9528(4) , and the renormalization-group dimensions of the operators that control the multicritical behavior are y_{1}=0.655(15) and y_{2}=0.250(2) ; they correspond to the thermal exponent nu identical with1/y_{2}=4.00(3) and to the crossover exponent phi identical withy_{1}/y_{2}=2.62(6) .