The acoustic attenuation for a one-band free-electron metal has been derived using a generalized scattering function. If the latter has an appreciable backward lobe, the attenuation exhibits an anomalous peak when the sound wavelength is comparable to the electron mean free path. Similar effects might be observable in the alkalis as a result of umklapp scattering processes. If so, further study could enhance our understanding of the electron-phonon interaction in these metals.

• Received 9 April 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.886