Two-point correlations in random uniaxial systems at marginal dimensionality

Abstract

The two-point correlation function for a random Ising model at d=4 is obtained using the solutions of the renormalisation-group recursion relations in the range of temperatures where the system exhibits non-asymptotic critical behaviour, the origin of which lies in a particular degeneracy of the RG recursion relations. The effects of lattice compressibility are also studied with two types of boundary conditions, corresponding to constant volume and pressure, respectively. A comparison with pure Ising systems is made.