Lattice melting at the clearing point in frustrated systems

This communication was stimulated by a meeting of the Sonderforschungsbereich 335, ‘Anisotrope Fluide’ at the Technische Universitat Berlin, in December 1994. At this conference we realized that there are some very strong similarities between the melting processes of blue phases, twist grain boundary phases, and cubic D phases to the isotropic, amorphous liquid. In all three cases the melting appears to be a two stage process with a sharp melting enthalpy followed by a broad diffuse endotherm as the disorganized liquid is formed. In this article we wish to draw attention to similarities in the nature of these melting processes, to suggest a general descriptive model for the breakdown in molecular ordering, and to stimulate a theoretical debate in order to gain an understanding of the role of frustration phenomena in melting processes.