Eigenstates of soft-mode vibrational excitations in thin-film metallic glasses

The vibrational excitations in Cu50Zr50 thin-film metallic glasses are investigated using molecular dynamics simulations. A strong density layering parallel to surfaces is formed in the glassy thin films. This layering behavior results in a layerlike arrangement of soft regions through films. The vibrational excitations in the periodic soft layers are proved to be harmonic and in analog y with the simple one-dimensional lattice vibration. A low-frequency and optical-like phonon mode features the soft-mode excitations. The soft-mode excitations enhance the vibrational density of states in the low-frequency side, depending on the softness of layers. Our results provide direct evidence supporting the low-frequency and nonacoustic vibrational excitations of soft domains in glasses.