Electric susceptibility

The electric susceptibility χe\chi_{e} is a dimensionless constant of proportionality associated with a type of dielectric material that describes the intensity of dielectric polarization in response to an external electric field. The greater the susceptibility, the greater the polarization. It is combined with the permittivity of free space to determine the material's permittivity.

The value of χe\chi_{e} depends on the microscopic structure of the material, as well as external factors like temperature. For a more general case, it's possible in some material that the value χe\chi_{e} depends on the direction too. Such materials are said to be anisotropic with respect to polarization. In this case, the susceptibility is described by the susceptibility tensor:

(χxxχxyχxzχyxχyyχyzχzxχzyχzz)\begin{pmatrix} \chi_{xx} & \chi_{xy} & \chi_{xz} \\ \chi_{yx} & \chi_{yy} & \chi_{yz} \\ \chi_{zx} & \chi_{zy} & \chi_{zz} \end{pmatrix}