Internal friction of vitreous silica measured with a double paddle oscillator

A double-paddle oscillator was used to measure the internal friction of vit reous silica at very low temperatures. The advantages of this experimental technique are the low background loss and the possibility to perform measur ements at different eigenmodes of the oscillator. Below 30 mK the internal friction was found to vary as T-z. Surprisingly, the exponent a increases m onotonically with frequency and varies between 0.85 at 0.33 kHz and 1.74 at 5 kHz. (C) 2000 Elsevier Science B.V. All rights reserved.