Quantum diffusion and localization in molecular crystals

The quantum diffusion of interstitial muonium atoms in crystals which under go orientational order-disorder phase transitions has been studied using th e technique of muonium-spin relaxation. In the high-temperature disordered phase, muonium dynamics becomes band-like with decreasing T. In contrast, i n the orientational glass phase the coherence is destroyed. At low temperat ures, both in the orientationally ordered phase, and in the orientational g lass phase muonium undergoes strong localization. (C) 2000 Elsevier Science B.V. All rights reserved.