anisotropy

The opposite of isotropy, i.e. the property of not being locally invariant under rotation.

For example, wood is anisotropic because it has grain; it is much easier to cut along the grain than against it.

Cosmologists got very excited&when they discovered that the Universe's background radiation is anisotropic.

in physics, the quality of exhibiting properties with different values when measured along axes in different directions. Anisotropy is most easily observed in single crystals of solid elements or compounds, in which atoms, ions, or molecules are arranged in regular lattices. In contrast, the random distribution of particles in liquids, and especially in gases, causes them rarely, if ever, to be anisotropic.

A familiar example of anisotropy is the difference in the refractive index of light along different axes of crystals of the mineral calcite. Another example is the electrical resistivity of selenium, which is high in one direction but low in the other; when an alternating current is applied to this material, it is transmitted in only one direction (rectified), thus becoming a direct current.

Anisotropy is of great value in the creation of high-temperature superconductors. A lot of low-temperature physics is performed on materials consisting of thin films, often manufactured through vacuum deposition of material onto a substrate or through lithography. The reason this is important relates to the Meissner effect, which, at the point of its breakdown at the high-magnetic-field limit, becomes a series of quantized magnetic-field vortices penetrating the superconducting material, and coupling very strongly to anisotropies in the material, such as crystalline breaks or lithographed impurities.