Critical Behavior of Anisotropic Cubic Systems

The critical behavior in zero field above Tc of ferromagnets or ferroelectrics with a Hamiltonian of cubic symmetry is studied, to order ε², by exact renormalization-group techniques in d=4-ε dimensions with n-component spins. For ε=1, n≥3, a crossover from isotropic (Heisenberg) to characteristic cubic behavior occurs, with the new value 2vC=1+[(n-1)3n]ε+[(n-1)324n³](17n²+290n-424)ε²+O(ε³), and cubic symmetry appearing in the four-spin correlation function. Experiments on structural phase transitions are considered briefly.