INTRINSIC ELECTRIC-DIPOLE MOMENT OF TUNNELING SYSTEMS IN SILICA GLASSES

Coherent electric echo magnitudes and decay rates have been studied systematically in four silica glasses with differing OH concentrations at a frequency of 0.7 GHz and to temperatures as low as 19 mK. Echoes have been observed in glasses with negligible OH content and originate from intrinsic tunneling systems possessing a mean electric dipole moment of approximately 0.5 D. We show that the OH in fused silica is associated with a distinct extrinsic tunneling species with a larger dipole moment and weaker phonon coupling. © 1979 The American Physical Society.