Dielectric Echoes in KBr KCN

We have observed electric dipolar echoes in the orientational glass KBr.50KCN.50 at 0.8 GHz. The low-energy excitations producing glassy behavior in this material at low temperatures have been explained previously as 180 degrees flips of the randomly oriented CN molecules. In our work the dephasing time T2 and the spin=lattice relaxation time T1 of these reorienting CN dipoles were measured using two-pulse and three-pulse echo techniques in the temperature range 5 to 60mK. The two-pulse experiment yielded exponential decays with T2 equivalent 20us at 5mK. The three-pulse decay is better approximated by a power law with an exponent of about -1 at 5mK. Spectral diffusion was found to play an important role in the decay process, as is typical of glassy systems. We will compare these results with similar measurements on samples of lower CN concentrations.