## Quick Reference

A quantum mechanical version of the Hall effect found at very low temperatures, in which the Hall coefficient *R*_{H} is proportional to *h*/*e*^{2}, where *h* is the Planck constant and *e* is the charge of the electron. Thus, the Hall coefficient is quantized. There are two types of quantum Hall effect. The **integer quantum Hall effect** has *R*_{H} given as an integer with great precision. It can be used for precision measurements of constants such as *e* and *h*. In the **fractional quantum Hall effect**, *R*_{H} has fractional values.

The integer quantum Hall effect can be understood in terms of noninteracting electrons, whereas the fractional effect is thought to result from many-electron interactions in two-dimensional systems, and be an example of anyons (see quantum statistics).

Analogues of the quantum Hall effect exist for spin; see spin Hall effect.

*Subjects:*
Physics.

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