Brillouin zone

In mathematics and solid state physics, the first Brillouin zone (named after Léon Brillouin) is a uniquely defined primitive cell in reciprocal space. In the same way the Bravais lattice is divided up into Wigner–Seitz cells in the real lattice, the reciprocal lattice is broken up into Brillouin zones. The boundaries of this cell are given by planes related to points on the reciprocal lattice. The importance of the Brillouin zone stems from the description of waves in a periodic medium given by Bloch's theorem, in which it is found that the solutions can be completely characterized by their behavior in a single Brillouin zone.

The first Brillouin zone is the locus of points in reciprocal space that are closer to the origin of the reciprocal lattice than they are to any other reciprocal lattice points (see the derivation of the Wigner–Seitz cell). Another definition is as the set of points in k-space that can be reached from the origin without crossing any Bragg plane. Equivalently, this is the Voronoi cell around the origin of the reciprocal lattice.

There are also second, third, etc., Brillouin zones, corresponding to a sequence of disjoint regions (all with the same volume) at increasing distances from the origin, but these are used less frequently. As a result, the first Brillouin zone is often called simply the Brillouin zone. In general, the n-th Brillouin zone consists of the set of points that can be reached from the origin by crossing exactly n − 1 distinct Bragg planes. A related concept is that of the irreducible Brillouin zone, which is the first Brillouin zone reduced by all of the symmetries in the point group of the lattice (point group of the crystal).

The concept of a Brillouin zone was developed by Léon Brillouin (1889–1969), a French physicist.

Within the Brillouin zone, a constant-energy surface represents the loci of all the -points (that is, all the electron momentum values) that have the same energy. The Fermi surface is a special constant-energy surface that separates the unfilled orbitals from the filled ones at zero Kelvin.

Critical points

Several points of high symmetry are of special interest – these are called critical points.

SymbolDescription ΓCenter of the Brillouin zone Simple cube MCenter of an edgeRCorner point XCenter of a face Face-centered cubic KMiddle of an edge joining two hexagonal facesLCenter of a hexagonal face UMiddle of an edge joining a hexagonal and a square faceWCorner point XCenter of a square faceBody-centered cubic HCorner point joining four edges NCenter of a face PCorner point joining three edges Hexagonal ACenter of a hexagonal face HCorner point KMiddle of an edge joining two rectangular faces LMiddle of an edge joining a hexagonal and a rectangular face MCenter of a rectangular face Other lattices have different types of high-symmetry points. They can be found in the illustrations below for both three- and two-dimensional lattices.

Brillouin zone types in 3D Lattice system Bravais lattice (Abbreviation) Triclinic Primitive triclinic (TRI) Triclinic Lattice type 1a (TRI1a) Triclinic Lattice type 1b (TRI1b) Triclinic Lattice type 2a (TRI2a) Triclinic Lattice type 2b (TRI2b)Monoclinic Primitive monoclinic (MCL) Monoclinic Lattice (MCL) Base-centered monoclinic (MCLC) Base-centered monoclinic lattice type 1 (MCLC1) Base-centered monoclinic lattice type 2 (MCLC2) Base-centered monoclinic lattice type 3 (MCLC3) Base-centered monoclinic lattice type 4 (MCLC4) Base-centered monoclinic lattice type 5 (MCLC5) Orthorhombic Primitive orthorhombic (ORC) Simple orthorhombic lattice (ORC) Base-centered orthorhombic (ORCC)Base-centered orthorhombic lattice (ORCC) Body-centered orthorhombic (ORCI) Body-centered orthorhombic lattice (ORCI) Face-centered orthorhombic (ORCF) Face-centered orthorhombic lattice type 1 (ORCF1) Face-centered orthorhombic lattice type 2 (ORCF2) Face-centered orthorhombic lattice type 3 (ORCF3) Tetragonal Primitive tetragonal (TET) Simple tetragonal lattice (TET) Body-centered Tetragonal (BCT) Body-centered tetragonal lattice type 1 (BCT1) Body-centered tetragonal lattice type 2 (BCT2) Rhombohedral Primitive rhombohederal (RHL) Rhombohedral lattice type 1 (RHL1) Rhombohedral lattice type 2 (RHL2) Hexagonal Primitive hexagonal (HEX) Hexagonal lattice (HEX) Cubic Primitive cubic (CUB) Simple cubic lattice (CUB) Body-centered cubic (BCC) Body-centered cubic lattice (BCC) Face-centered cubic (FCC) Face-centered cubic lattice (FCC)

Brillouin zone types in 2D Sources:

In two dimensions, the number of Bravais lattices reduces to five. In the following illustration, the corresponding Brillouin zones are delimited by red lines.

For each lattice, the irreducible Brillouin zone is highlighted (blue) in accordance with the definitions of the symmetry points given in Refs. and .

Brillouin zone

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