Sometimes the most arresting aspect of a natural object is its symmetry. The delicate and complex contours of a snowflake, for example, are all the more fascinating because of the crystal’s symmetrical branches. The sixfold rotational symmetry of a snowflake comes from the hexagonal structure of the ice crystal that, in turn, is related to the shape and orientation of the bonded water molecules.
In molecular materials like water, the structural units that make up the liquid state can also dictate the properties of the frozen solid. But what about monatomic liquids that are composed of single atoms, rather than molecules? It is tempting to think of such liquids as completely unstructured, like gases in slow motion, but this is not the case.
In the March issue of Physics World, Elaine DiMasi of Brookhaven National Laboratory, USA, describes a successful search for fivefold symmetric clusters in liquid lead by Harald Reichert at the Max Planck Institute in Stuttgart, Germany, and colleagues from Germany, France and the US (Nature 2000 408 839).
