Abstract
We have measured the sound velocity and attenuation of polycrystalline Cu, Al, Nb, Nb 48 Ti 52 , Pt, P 20 Rh 30 , Pt(l%W), Pd, Ta, NiCr alloy and amorphous PdSiCu at frequencies 0.1 kHz < v < 20 kHz and at temperatures 40 mK < T < 10K. All polycrystalline samples show acoustic properties which resemble those of dielectric glasses. Their electrical resistivity is in the range 10- 10 Ωm < p < 10 -5 Ωm with an estimated electron mean free path of 10- 10 m < l< 10 -5 m. Our results indicate no correlation between the tunneling system density of states or coupling constant and the electron mean free path, supporting earlier work on the absence of electron assisted relaxation rate. For polycrystalline metals we found that the ratio T∞ / v 1/3 (0.006 ± 0.002) K/Hz 1/3 in agreement with dielectric glasses (T∞ is the temperature at the sound velocity maximum).
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