Electron localization in a disordered insulating host

Transport of excess electrons has been studied in solid N2-Ar mixtures between 5 and 60 K using muon spin rotation in magnetic and electric fields. At low temperatures, orientational frustration of N2 molecular quadrupoles by a sufficiently high concentration of Ar atoms leads to formation of a quadrupolar glass phase in which electrons are found to be strongly localized. This feature is in marked contrast to the electron delocalization observed in the low-temperature alpha phase of pure solid nitrogen, which shows long-range orientational order.