EPJ E Colloquium - Hidden order in the liquid phase

A snapshot of 2D spin liquid in a supercooled state. (Fig. 3 from the paper)

A two-order parameter model proposed to describe water-like anomalies, liquid-liquid transition, glass transition, crystal nucleation and quasicrystal formation within the same framework.

The liquid state of matter is far from being a perfectly disordered homogeneous state. In a Colloquium paper published in EPJ E, Hajime Tanaka argues that to achieve a better understanding of liquids, it is crucial to recognize that a liquid has a general tendency to exhibit local structural order, and that this order is intrinsic and universal to any liquid. In other words, there is a need for a new order parameter describing a low local free-energy configuration (this is a bond-orientational order parameter in many cases), in addition to a density order parameter.

Tanaka describes a model based on these two order parameters and proposes that this facilitates the physical description of phenomena in the liquid state and may lead to a unified description of important unsolved problems in our understanding of the liquid state, such as anomalies associated with water-type liquids (water, Si, Ge, etc.), liquid-liquid transitions, liquid-glass transitions, crystallization and quasicrystal formation. The Colloquium takes into consideration how transient local structural order is related to all of the aforementioned phenomena and how these phenomena are related to each other. The model contains speculative arguments that invite further experimental, numerical and theoretical studies to explore the physical picture it provides.