Commonalities in frequency-dependent viscoelastic damping in glasses in the MHz to THz regime

Abstract

We use non-equilibrium molecular dynamics oscillatory shear simulations to study frequency-dependent viscoelastic damping spanning nearly six decades in frequency range (MHz to THz), in a wide range of model glasses including binary glasses such as Cu-Zr metallic glass (MG), Wahnström glass and amorphous silica, and unary glasses, namely, Dzugutov glass and amorphous silicon. First, for the Cu-Zr MG, we elucidate the role of quench rate, number of shear cycles, shear amplitude, and shear temperature on the damping characteristics. We observe striking commonalities in damping characteristics for all glasses studied—(i) a peak in the loss modulus in the high-frequency regime (∼THz) and (ii) persistent damping in the low-frequency regime (extending down to 10 s of MHz). The high-frequency peak is seen to overlap with the range of natural vibrational frequencies for each glass, and arises from coupling between the excited harmonic vibrational modes. On the other hand, persistent damping at intermediate and low frequencies is shown to be a result of long time-scale local, irreversible deformation.