NONEQUILIBRIUM PHENOMENA IN SPECTRAL DIFFUSION PHYSICS OF ORGANIC GLASSES

We performed two different types of spectral diffusion experiments on persistent spectral holes. In all cases, we measured the holewidth as a function of time. The two experiments differed in their initial cond itions: In the type 1 experiment (the ''aging experiment''), the sampl e was cooled from room temperature to the final temperatures which wer e 100 and 800 mK, respectively. Holes were burnt at various time inter vals after the final temperature was reached. In the type 2 experiment (the ''cycling experiment''), the sample was allowed to relax for a p eriod of about 10 days. Then, a hole was burnt and subjected to a temp erature cycle. In ail cases, the time dependence of the holewidths was strongly nonlogarithmic. The temperature cycled hole showed a narrowi ng regime which prevailed for the whole observation period of roughly one week. We will show that the deviation from the logarithmic time de pendences is a nonequilibrium phenomenon. All features observed could be modelled within the standard tunneling model. (C) 1996 American Ins titute of Physics.