It was shown that a generic long-range correlated disorder that arose in real crystals, due to their almost unavoidable dislocation content, led to a breakdown of the conventional standard renormalization group techniques that were based upon the existence of a simple homogeneous ground state. This breakdown was due to the appearance of an inhomogeneous ground state which changed the nature of the phase transition into that of a percolation phenomenon. This conclusion led to a natural explanation for the appearance of 2 length-scales in high-resolution small-angle scattering experiments near to magnetic and structural phase transitions.

Inhomogeneous Ground State and the Coexistence of Two Length Scales near Phase Transitions in Real Solids. A.L.Korzhenevskii, K.Herrmanns, H.O.Heuer: Europhysics Letters, 1999, 45[2], 195-200