THE DISSIPATIVE DYNAMICS OF A PAIR OF PARAELECTRIC TUNNELING IMPURITIES

Paraelectric impurities contribute significantly to the low-temperatur e properties of alkali halide crystals. Even at very low density the d ipolar interaction of adjacent defect ions may lead to deviations from the behaviour expected for isolated impurities; in a certain range of concentration it is sufficient to consider pairs of coupled defects. Applying a projection operator method, previous work on this pair mode l is extended to the case of finite asymmetry and weak coupling to aco ustic phonons. After performing the ensemble averaging, the specific h eat and the zero-frequency susceptibility are calculated and compared with experimental data on KCl:Li and KCl:CN. The isotope effect on the Rabi frequency and relaxation rate is discussed.