Relaxation of Tunneling Systems by Conduction Electrons in a Metallic Glass

Acoustic experiments on the metallic glass Pd0.775{Si}0.165Cu0.06 are presented which show a tunneling-system decay rate at 0.01 K enhanced by a factor of 10⁴ over insulating glass. A theory is presented for decay based upon the coupling of tunneling systems to conduction electrons, and the parameters of the theory are obtained from experiment. Relaxational absorption and dispersion in this amorphous metal are interpreted in terms of a tunneling model with a broad spectrum of decay rates.