Influence of Phonons and Electrons on Low-Temperature Translational Tunneling

Abstract

The model of a particle moving in a multistable potential is encountered in various fields of physics. At low temperatures transitions between adjacent wells involve quantum tunneling which is strongly influenced by the coupling of the particle to its environment. Recent studies have led to some progress in the theoretical description of this problem. For interstitials in metallic crystals the tunneling rate is affected by the coupling to conduction electrons and phonons. At very low temperatures the defect tunnels coherently. This band-like transport is destroyed near a typical crossover temperature above which subsequent tunneling transitions become statistically independent. The incoherent tunneling rate first decreases with increasing temperature as an effect of the electron cloud surrounding the defect. The rate then goes through a minimum above which phonon assisted tunneling dominates leading to an increase of the rate. The basic ideas underlying the theoretical treatment of defects in metals and some recent theoretical predictions are presented.

on leave from: Institut für Theoretische Physik, Universität Stuttgart, D-7000 Stuttgart 80, Germany