INTERACTING TUNNELING STATES - A HOLE-BURNING STUDY OF SPECTRAL DIFFUSION

Performing long-time thermal equilibrium measurements of spectral diff usion broadening of photochemical holes, we recently established an al gebraic time dependence of the dynamics of two-level system (TLS), whi ch we interpret in terms of TLS-TLS coupling (Phys. Rev. Lett. 76 (199 6) 2085). For this purpose we utilized the continuous cooling property of our He-3/He-4 cryostat. To extend the accessible temperature range we have constructed a cryostat which allows optical experiments lasti ng several weeks at temperatures of 1.5K and above. Here we report dat a obtained at 2.0K in a time range from 10 s to 10(6) s. Interpreted i n the framework mentioned above, the results indicate the onset of a t hermally induced break-up of the TLS-TLS coupling.