Intrinsic Electric Dipole Moment of Tunneling Systems in Silica Glasses

Abstract

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.