Boson-peak-like anomaly caused by transverse phonon softening in strain glass

Strain glass is a new glassy state characterized by frozen ferroelastic nanodomains. Here, the authors discover a low-temperature feature in the specific heat of a strain glass, which is similar to the well-known boson peak anomaly of structural glasses, but cannot be explained by existing mechanisms. Strain glass is a glassy state with frozen ferroelastic/martensitic nanodomains in shape memory alloys, yet its nature remains unclear. Here, we report a glassy feature in strain glass that was thought to be only present in structural glasses. An abnormal hump is observed in strain glass around 10 K upon normalizing the specific heat by cubed temperature, similar to the boson peak in metallic glass. The simulation studies show that this boson-peak-like anomaly is caused by the phonon softening of the non-transforming matrix surrounding martensitic domains, which occurs in a transverse acoustic branch not associated with the martensitic transformation displacements. Therefore, this anomaly neither is a relic of van Hove singularity nor can be explained by other theories relying on structural disorder, while it verifies a recent theoretical model without any assumptions of disorder. This work might provide fresh insights in understanding the nature of glassy states and associated vibrational properties.

Automated summary

In this study, researchers discovered a low-temperature feature in strain glass that is similar to the well-known boson peak anomaly in structural glasses, but cannot be explained by existing mechanisms. This anomaly is caused by the phonon softening of the non-transforming matrix surrounding martensitic domains, and it verifies a recent theoretical model without assumptions of disorder. This finding may provide fresh insights into understanding the nature of glassy states and associated vibrational properties.