Phonon scattering by electrons in noncrystalline alloys

The low-temperature thermal conductivity of noncrystalline ${\mathrm{Zr}}_x{\mathrm{Be}}_{1-x}$ ($x\sim 0.5$) has been measured between 0.3 and 4 K. A pronounced decrease of the thermal conductivity near the superconducting transition temperature ($T_c\sim 2$ K) has been observed. In the entire temperature range studied, the thermal conductivity can be explained with the model that the Debye phonon mean free path is determined by scattering through the electrons and the intrinsic states which appear to be characteristic for all amorphous solids. The observed scattering of the phonons by the electrons can be explained with the theories developed for highly disordered crystalline metals and for superconductors near $T_c$.