In this article we demonstrate the importance of the indirect interaction via the phonon field between pairs of defects in an amorphous material. Using only the approximate value of the lattice coupling constant it is shown that the exchange interaction is large. The most important conclusion that can be drawn from this calculation is that the order of magnitude of the T 2 relaxation time of a spin packet is quite small (10-9 s). It is therefore not possible to interpret the experimental data under the hypothesis 2 T1 = T2 hitherto used; we re-analyse the available results from this new point of view
This paper presents a detailed study of the temperature dependence of the longitudinal relaxation time T I and of the coherence time T e o[ a population of ionic molecular impurities in silica glass. Electric dipolar echoes taken in a temperature range 4-22 mK and a frequency of 370 MHz show that T I isgoverned by a one-phonon process; consequently T~ vanes hke T ; expertmental data show that Te also vanes hke T and thts m contradtctton wtth predictions which lead to T -e. The relaxation of the spontaneous and stimulated echoes shows that there is a wide distribution of relaxation times (T I and Te); from the amplitude of the signal it is also possible to extract both the longitudinal and the transverse electric moment; the coupling constant of the impurities with the strain is found to be as large as 3 eV.
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