Unusual Phonon Heat Transport in an Amorphous SuperconductingPbCuFilm

We report thermal conductivity measurements of a ${\mathrm{Pb}}_{0.9}$ ${\mathrm{Cu}}_{0.1}$ film before (amorphous) and after (crystalline) annealing. Below $T_c$, where electronic effects are negligible, we found that the phonon contribution in the amorphous phase ${k_{\mathrm{am}}}^{\mathrm{ph}}$ was much larger than that in the crystalline phase. We also found that the temperature dependence of ${k_{\mathrm{am}}}^{\mathrm{ph}}$ resembles that of amorphous dielectrics, thus providing evidence that this sort of "glassy" behavior does not require the presence of covalent bonds.