Strongly correlated material

The essential feature that defines these materials is that the behavior of their electrons or spinons cannot be described effectively in terms of non-interacting entities.

Other ordering or magnetic phenomena and temperature-induced phase transitions in many transition-metal oxides are also gathered under the term "strongly correlated materials."

Typically, strongly correlated materials have incompletely filled d- or f-electron shells with narrow energy bands.

For instance, the seemingly simple material NiO has a partially filled 3d band (the Ni atom has 8 of 10 possible 3d-electrons) and therefore would be expected to be a good conductor.

However, strong Coulomb repulsion (a correlation effect) between d electrons makes NiO instead a wide-band gap insulator.