Low-Temperature Thermal Conductivity of Amorphous Germanium

The thermal conductivity $k$ of $a$-Ge films has been measured between 0.4 and 10 K. The temperature dependence of $k$ shows that heat conduction by phonons is limited by some intrinsic scattering mechanism in addition to boundary scattering. Evidence is presented that these scatterers are localized low-energy excitations which are common in glasses.