Neutron scattering and specific heat study of AlGe and AlSi alloys quenched under high pressure

Neutron scattering and specific heat measurements on pressure-quenched AlGe and AlSi alloys are reported. The neutron results corroborate earlier findings of a pronounced softening of the transverse zone boundary modes in these polycrystalline nonequilibrium alloys, reminiscent of a similar softening observed in metallic glasses. At lower frequencies, however, no pronounced glassy anomaly is found. The additional excitations seen around 9 meV in AlGe can be explained in terms of resonant modes of the heavier Ge atoms. At still lower frequencies, neutrons see only sound waves. The more sensitive specific heat technique shows the corresponding lattice T³ term and an electronic contribution which follows the classical BCS behaviour at the transition to superconductivity. Below 0.5 K, there remains a linear term about a factor of ten smaller than in typical glasses.