Localization, conductivity, and superconductivity

✍ Scribed by Sven Larsson; Agris Klimkāns

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 179 KB
• Volume: 80
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/1097-461x(2000)80:4/5<713::aid-qua21>3.0.co;2-1

✦ Synopsis

Electron localization is of great importance for the understanding of phonon coupling in ordinary conductivity and superconductivity. We discuss localization in "Mott insulators," but take a critical view on the Mott model, which explains localization on the basis of a disproportionation reaction, involving the Mott-Hubbard parameter U. Instead we emphasize electron-nuclear interactions in determining localization properties. Depending on the ratio between intersite coupling and reorganization energy, the nature of valence-state fluctuations range from localized, discrete hops between sites to delocalized transport, either barrierless hopping or phonon-coupled band motion. In the case of three stable oxidation states, there is a possibility for a conducting ground state with a finite energy gap to excited states. Finally we discuss the appearance of "giant magnetoresistance" as an example of delocalized mixed valence system in the metallic and ferromagnetic phase.