Unveiling the boson peak from local geometric distortion in a metallic glass

The origin of boson peaks is vital for understanding the nature of glasses, but remains unsettled. Applying molecular dynamics simulations, we clearly demonstrate that this mystery can be cracked by scrutinizing the individual vibration mode and the local symmetry of structure in glasses. The intensity of boson peaks can be significantly enhanced by vibrational modes with large vibrational amplitudes and high vibrational anisotropy. Furthermore, these vibrational modes are correlated to the structural motifs with a large number of types of local symmetry, which results in extensive local distortion. This local distortion contributes to the excess low-frequency vibration around the boson peak. Therefore, our findings shed light on the roles of local geometric distortion in understanding the structural origin of boson peaks.