Novel Class of Continuous Phase Transitions to Incommensurate Structures

Abstract

We present and analyze a new class of continuous phase transitions to incommensurate structures. This class is characterized by a small order parameter and diverging susceptibility, in common with instability-type transitions. However, the fundamental wave vector vanishes at the transition and the harmonic components of the order parameter are not small compared with the fundamental component, in common with nucleation-type transitions. These properties are shown to result from a gradient-cubic term in the free energy.