Nonacoustic high-frequency collective excitations in a ZrCuAl metallic glass

We report a combined theoretical and simulation study of collective excitations in the three-component metallic glass Zr46Cu46Al8. It is shown in that case how one can combine partial current time correlation functions to represent them via total mass and mass-concentration currents, which for the long-wavelength region separately describe hydrodynamic acoustic and nonhydrodynamic opticlike modes. We present dispersions of the longitudinal and transverse acoustic and optic modes over a wide range of wave numbers. Our theoretical analysis of dispersion and damping of three transverse short-wavelength modes sets the basis for the interpretation of already existing experimental data, where the presence of three modes has been disregarded leading to an overestimation of the alleged transverse mode damping.