Level repulsion and the dielectric relaxation in quadrupolar glasses

Dielectric relaxation in quadrupolar glasses is dominated at low temperatures by thermal activation over local anisotropy barriers produced by the quadrupolar freezing. The distribution of barrier heights V vanishes linearly as V→0 at all temperatures due to the repulsion of levels of the random internal stress tensor. A further shift of V to higher values occurs as T decreases due to correlations. These results are compared with recent dielectric measurements in (KBr${)}_{0.5}$(KCN${)}_{0.5}$.