plaquette

Plaquette is a term used in several disciplines to denote a small, flat plate or a plate-like element. The word comes from the French plaquette, a diminutive of plaque, meaning a small flat object.

In general use, a plaquette can be any small plate or plate-like piece of material, such as metal, stone, or ceramic, that is separate from a larger object and may carry inscriptions or adornment.

In materials science and metallurgy, a plaquette refers to a small, flat piece cut from a larger specimen for examination of its microstructure. Such samples are prepared to be thin and planar to facilitate microscopic analysis.

In physics and related areas, a plaquette denotes the smallest closed surface (usually a square) on a lattice. On a two-dimensional square lattice, the plaquette is the unit square bounded by four lattice points and their connecting links; in three dimensions it is a square face of a cubic lattice. Plaquettes are used to define gauge-invariant observables, such as Wilson loops, and to approximate field strengths in discretized models.

In tiling and lattice models, plaquettes can also refer to individual tiles or cells of a lattice or tessellation, often when discussing small clusters (for example, a 2×2 plaquette) in quantum or statistical mechanical contexts.

While related in spelling, plaquette should not be confused with plaque in the dental sense or with larger plaques in decorative use.