Mottinsulator

A Mott insulator is a material that, according to band theory, should be metallic because it has partially filled electronic bands, yet it behaves as an insulator due to strong electron-electron interactions.

In these systems, the dominant physics is described by the Hubbard model with on-site Coulomb repulsion U competing with the electron bandwidth W. When U is larger than W, electrons avoid double occupancy and localize on lattice sites, opening a correlation-induced gap at the Fermi level. The resulting state is called a Mott insulator or Mott–Hubbard insulator. The insulating state often coexists with magnetic order (e.g., antiferromagnetism) arising from superexchange between localized spins.

At half filling, a single electron per site, the system tends to localize; doping with carriers (holes or electrons) can close the gap and drive a transition to a metallic or superconducting state, a phenomenon known as the Mott metal-insulator transition. The transition can be first-order in some materials, and can be tuned by temperature, pressure, or chemical substitution.

Prototypical examples include transition metal oxides such as NiO, MnO, FeO, and V2O3, as well as the parent compounds of cuprate superconductors like La2CuO4. In many nickelates and cuprates, strong correlations determine the low-energy physics.

Theoretical treatments include the Hubbard model and its strong-coupling derivatives (t-J model); dynamical mean-field theory (DMFT) provides a framework to study the transition and spectral properties.