ABSTRACT
We have shown in this review that, in order to arrive at exotic Kondo states which display non-Fermi-liquid fixed points, the minimal generalization of the single channel Kondo model is via the addition of channel or flavour quantum numbers to the conduction electrons. The two-channel https://www.w3.org/1998/Math/MathML"> s p i n 1 2 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003062783/c3a2fb10-3fa7-419c-b821-2aafea3c6343/content/inline-math707.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> Kondo model obtained in this way has been shown to describe a great variety of physical phenomena from disparate areas of condensed matter physics, such as amorphous metals, nanometer scale point contact devices, certain rare-earth and transition-metal ions in metals (some of which become exotic superconductors at full concentration of the ions), and quantum dots in the Coulomb blockade regime. In particular, it is apparent that any time a local pseudo-spin degree of freedom is non-magnetic, a mapping to a two-channel Kondo model is possible in which the channel degree of freedom is the magnetic spin or time reversal index of the conduction electrons, guaranteed to be degenerate in the absence of magnetic field by Kramers theorem. Given this broad variety of possibilities, we can only anticipate that new models and experimental systems will be discovered for which a mapping to a model with a non-Fermi-liquid fixed point will be on solid ground.
