Mott insulator

As Mott insulators materials are referred to, which actually should be electrically conductive after the band model, but prove in the experiment as insulators. The name goes back to the British physicist Sir Nevill F. Mott, who grappled with this phenomenon. An example of a Mott insulator is nickel ( II) oxide.

History

In 1974 predicted Mott states of matter in which the central assumption of the band model - each electron moves independently and feel the presence of the other electrons only on the basis of an averaged potential - no longer applies. This is due to slight interactions between the electrons resulting from the classical Coulomb repulsion between particles of the same charge. They lead to a change in the periodic potential of the atoms: Increase the individual potential barriers located. This plays a crucial role, in which Coulomb barrier and delocalized electrons are in a sensitive balance, especially in such solids. Even small changes in the potential shape or height call them forth at metal - insulator transitions. The conduction electrons can not move freely through the crystal itself. They behave like spatially localized, bound to individual atoms and particles are placed in the altered energy landscape in the potential wells like eggs in an egg carton. The material is an insulator.

Mott insulators are ideally suited to investigate fundamental issues in solid state physics and atomic physics, including the individual interaction of the electrons with each other under predefined conditions. They also play a role in some theories to explain high-temperature superconductors.

Production

Metal - insulator transitions from the Mott - type can cause, for example, by changing the pressure or by doping with foreign atoms. If you increase the pressure in a non-conducting sample, the distance of the ( ionized ) atoms is lower. To the same extent, the number of free electrons and their mutual interference is increased. In a material-dependent critical pressure, the conduction electrons are released abruptly, and the solid becomes a metallic conductor. Endowed one semiconductor such as silicon carbide or gallium arsenide with suitable materials also increased the number of electrons. After the band model of a metal should have arisen, however, interactions between the electrons after the Mottmodell allow the material to be an insulator.

A completely different class of Mott insulators can be realized using thin surface layers. In extended solids gains in general the tendency of electron delocalization the upper hand and turns them into electrical conductors. If one limits the electrons but spatially one, for example, the extremely thin surface layer of a semiconductor, a Mott insulator should arise. In the 1990s, a systematic search began for such materials. A classic experiment is the production of an Mott insulator on a silicon surface. Implanted boron provides for an initial electron depletion, then potassium absorbed until enough electrons are available to achieve metallic conductivity after Bloch Wilson Model. For the investigation of the electronic configuration of potassium -covered silicon surface is irradiated with ( short-wavelength ) light, the electron knocks out from the material. The energy distribution of the emitted photoelectrons has a significant band gap between the filled and empty energy bands, the characteristic of an insulator.

In 2002, Munich scientists first reported by the conversion of a Bose -Einstein condensate (BEC ) in a Mott insulator near the absolute zero point. The researchers began the superfluid quantum collective into a three-dimensional network of laser beams and thereby urged its members to well-defined lattice sites. The community was divided into individual atoms, which were locked up in individual troughs. With the laser grid could also be the depth as well as the periodicity of the energy landscape changed arbitrarily and thus switched between the Mott insulator and a Bose -Einstein condensate back and forth. Such Mott insulators open as switching and computing elements new perspectives on the way to a quantum computer.