Acoustic resonance in periodically sheared glass

Using molecular dynamics simulation, we study acoustic resonance in low-temperature glass by applying a small periodic shear at a boundary wall. Shear wave resonance occurs as the frequency $\omega$ approaches $\omega_\ell= \pi c_\perp\ell/L$ ($\ell=1, 2, 3,...)$. Here, $c_\perp$ is the transverse sound speed and $L$ is the cell length. At resonance, large-amplitude sound waves appear after many cycles even for very small applied strains. They then induce plastic events, which are heterogeneous in space and intermittent on time scales longer than the oscillation period $2\pi/\omega$. From these irreversible particle motions, there arises strong dissipation suppressing the growth of sounds. After many resonant cycles, we observe a phenomenon of forced aging, where the shear modulus (measured after switching off the oscillation) is increased significantly.Sometimes, exceptionally large plastic events and system-size sliding motions induce a transition from resonant to off-resonant states. At resonance, translational diffusion becomes appreciable as well as aging due to enhanced configurational changes.