Abstract
The phonon thermal conductivity χph(T < 1 K) is measured on a series of amorphous Pd77.5Cu6Si16.5 samples prepared with different quenching rates q. The density of low-energy excitations (LEE) n times the coupling parameter γ2 as inferred from χph(T) increases with q. Using calculated values for the frozen-in free volume vf as a function of q, a monotonic increase of nγ2 with vf is found. The same result is found, when vf (or the mass density) is changed by structural relaxation of plastic deformation. These findings give direct evidence for the validity of the free-volume model explaining the origin of LEE in metallic glasses.
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