Although the band theory of solids had been very successful in describing various electrical properties of materials, in 1937 Jan Hendrik de Boer and Evert Johannes Willem Verwey pointed out that a variety of transition metal oxides predicted to be conductors by band theory are insulators.
[1] Nevill Mott and Rudolf Peierls also in 1937 predicted the failing of band theory can be explained by including interactions between electrons.
[3] In 1949, in particular, Mott proposed a model for NiO as an insulator, where conduction is based on the formula[4] In this situation, the formation of an energy gap preventing conduction can be understood as the competition between the Coulomb potential U between 3d electrons and the transfer integral t of 3d electrons between neighboring atoms (the transfer integral is a part of the tight binding approximation).
In general, Mott insulators occur when the repulsive Coulomb potential U is large enough to create an energy gap.
The crossover from a metal to a Mott insulator as U is increased, can be predicted within the so-called dynamical mean field theory.
[5] The subject has been thoroughly reviewed in a comprehensive paper by Masatoshi Imada, Atsushi Fujimori, and Yoshinori Tokura.
If the criterion is satisfied (i.e. if the density of electrons is sufficiently high) the material becomes conductive (metal) and otherwise it will be an insulator.
[8] Mottism denotes the additional ingredient, aside from antiferromagnetic ordering, which is necessary to fully describe a Mott insulator.
There are a number of properties of Mott insulators, derived from both experimental and theoretical observations, which cannot be attributed to antiferromagnetic ordering and thus constitute mottism.
Due to electric field screening the potential energy becomes much more sharply (exponentially) peaked around the equilibrium position of the atom and electrons become localized and can no longer conduct a current.
Mott argued that the transition must be sudden, occurring when the density of free electrons N and the Bohr radius
Simply put, a Mott transition is a change in a material's behavior from insulating to metallic due to various factors.
As observed by Nevill Francis Mott in his 1949 publication on Ni-oxide, the origin of this behavior is correlations between electrons and the close relationship this phenomenon has to magnetism.
The physical origin of the Mott transition is the interplay between the Coulomb repulsion of electrons and their degree of localization (band width).
When the transport of carriers overcomes a minimum activation energy, the semiconductor has undergone a Mott transition and become metallic.
Mott insulators are of growing interest in advanced physics research, and are not yet fully understood.
They have applications in thin-film magnetic heterostructures and the strong correlated phenomena in high-temperature superconductivity, for example.
[17][18][19][20] This kind of insulator can become a conductor by changing some parameters, which may be composition, pressure, strain, voltage, or magnetic field.
The effect is known as a Mott transition and can be used to build smaller field-effect transistors, switches and memory devices than possible with conventional materials.