Low-frequency vibrational anomalies induced by anharmonic interactions in metallic glasses and crystals

Low-frequency vibrational anomalies, such as the “boson peaks” observed in a number of glasses and several crystals, has attracted considerable research interest, yet the nature and origin of the anomaly are still a subject of intense debate. Here, we calculate and compare the vibrational density-of-states with and without anharmonic interactions for two realistic intermetallic systems (Al-Ce and Al-Tb) in both glassy and crystalline phases. We demonstrate that low-frequency vibrational anomalies can arise in both bulk glassy and crystalline structures as long as anharmonic interactions are included. Moreover, in contrast to previous proposal which attributes boson peaks to localized (or quasi-localized) vibrational modes associated with the low-density defective structures in amorphous materials , we show that almost all atoms in the metallic glass samples are associated with the low-frequency vibrational anomalies, and atoms with higher local order propensity tend to contribute more to the anomaly.