Ordinary tiles form a repeating pattern. But atoms can do more: under certain conditions, they themselves lay out a complex mosaic where the pattern never repeats, like on antique tile panels.
In a recent experiment, two types of atoms cooled to a joint wave state (a phenomenon predicted by Einstein) were trapped in a crosshatch of laser beams. When their mutual repulsion became strong, glow observations and pulse measurements revealed a pattern with eightfold symmetry. This is a hallmark of a quasicrystal — a structure with order but no repetition, unlike a crystal lattice.
An ordinary crystal, like wallpaper, consists of identical cells. A quasicrystal is more like a mosaic where no fragment repeats exactly, but the overall design is harmonious. The stability of such an atomic mosaic requires equal numbers of both types of atoms. The slightest imbalance destroys the pattern. From the standpoint of a measure of disorder, the system first loses regularity but then finds a more sophisticated packing scheme. Most surprising: such patterns, once considered a mathematical abstraction, were first discovered in meteorite material, and now they are created in the lab using only light and cold.
Eightfold symmetry is forbidden for ordinary crystals, so quasicrystals, first produced in 1982, became a scientific sensation. Later such structures were found in meteorites, showing that nature can create the impossible.