Metal-insulator transition

Metal-insulator transitions refer to changes in the transport properties of a given material. Roughly speaking, materials can be classified as metals, allowing for good conductivity of electric charges, and as insulators, where conductivity of charges is quickly suppressed. In some materials, most notably semiconductors, changing their ambient conditions by, e.g. applying pressure or gate voltages, one can tune the transport properties from metallic to insulating or vice versa. These materials are thus useful as controlling devices in electric and electronic circuits.

Theoretical understanding of metal-insulator transitions elucidates roughly 3 classes of metal-insulator transitions. Doping a material can change its internal electronic structure, giving rise to or eliminating band gaps. Materials in which a band gap prohibits electronic conductivity are call band-gap insulators. Electron-electron interaction can also lead to the opening of an interaction-induced gap, the so-called Mott-Hubbard gap. Disorder in the material composition can lead to Anderson localization which prohibits conductivity. This is a disorder-induced metal-insulator transition even without any band gap.

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* [http://www2.warwick.ac.uk/fac/sci/csc/images/wf111.jpgExample of an electronic eigenstate at the MIT in a system with 1367631 atoms. Each cube indicates by its size the probability to find the electron at the given position. The color scale denotes the position of the cubes along the axis into the plane]