Effects of in-band defect-induced phonon resonant modes on phonon-assisted defect tunneling

Abstract

Transition rates for off-center or molecular-defect reorientations show polaron-like effects with one- or fewphonon assisted tunneling at low temperatures becoming Arrhenius-like processes at higher temperatures. Perturbation of the phonons by heavy and/or loosely coupled defects can produce in-band resonant modes. A simple model is used to show that such resonant modes can have significant effects on transition rates and, in particular, can extend the range of Arrhenius behavior to temperatures substantially lower than those predicted by modesl which use Debye phonons unaltered by the presence of the defect.