Numerical study of the transition of the four dimensional Random Field Ising Model

Abstract

We study numerically the region above the critical temperature of the four dimensional Random Field Ising Model. Using a cluster dynamic we measure the connected and disconnected magnetic susceptibility and the connected and disconnected overlap susceptibility. We use a bimodal distribution of the field with $ h_R=0.35T $ for all temperatures and a lattice size L=16. Through a least-square fit we determine the critical exponents $ \gamma $ and $ \bar{\gamma} $. We find the magnetic susceptibility and the overlap susceptibility diverge at two different temperatures. This is coherent with the existence of a glassy phase above $ T_c $. Accordingly with other simulations we find $ \bar{\gamma}=2\gamma $. In this case we have a scaling theory with two indipendet critical exponents