Low-temperature internal friction in metal films and in plastically deformed bulk aluminum

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Abstract
Crystalline metal films on silicon substrates have been found to have a surprisingly large, nearly temperature-independent internal friction at low temperatures, with a magnitude similar to that of amorphous solids. This large internal friction is rather insensitive to chemical composition and impurities, mode of film preparations, and film thickness, but can be reduced considerably by proper alloying. In an attempt to understand its origin, plastically deformed bulk aluminum has been measured in the superconducting state. It has been found that its internal friction can be increased over two orders of magnitude by plastic deformation. For deformations exceeding 10% the internal friction saturates and resembles that of the metal films both in magnitude and temperature independence. It is suggested that the damping is caused by a broad spectrum of tunneling states associated with dislocations both in the bulk metal and in the metal films.

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