Inhomogeneous ground state and the coexistence of two length scales near phase transitions in real solids

Abstract

Real crystals almost unavoidably contain a finite density ofdislocations. We show that this generic type of long-range correlateddisorder leads to a breakdown of the conventional scenario of criticalbehavior and standard renormalization group techniques based on theexistence of a simple, homogeneous ground state. This breakdown is dueto the appearance of an inhomogeneous ground state that changes thecharacter of the phase transition to that of a percolative phenomenon.This scenario leads to a natural explanation for the appearance of twolength scales in recent high resolution small-angle scatteringexperiments near magnetic and structural phase transitions.