MONTE-CARLO STUDY OF THE YUKAWA COUPLED 2-SPIN ISING-MODEL

We consider a particular four state spin system composed of two Ising spins (s(x), sigma(x)) with independent hopping parameters kappa(1), k appa(2), coupled by a bilinear Yukawa term, ys(x) sigma(x). The Yukawa term is solely responsible for breaking the global Z(2) X Z(2) symmet ry down to Z(2). This model is intended as an illustration of general coupled Higgs system where scalers can arise both as composite and ele mentary excitations. For the ising example in 2d, we give convincing n umerical evidence of the universality of the two-spin system with the one-spin Ising model, by Monte Carlo simulations and finite size scali ng analysis. We also show that as we approach the phase transition, un iversality arises by having a single correlation length that diverges.