  The low temperature heat capacity of amorphous materials reveals a
low-frequency enhancement (boson peak) of the vibrational density of states, as
compared with the Debye law. By measuring the low-temperature heat capacity of
a Zr-based bulk metallic glass relative to a crystalline reference state, we
show that the heat capacity of the glass is strongly enhanced after severe
plastic deformation by high-pressure torsion, while subsequent thermal
annealing at elevated temperatures leads to a significant reduction. The
detailed analysis of corresponding molecular dynamics simulations of an
amorphous Zr-Cu glass shows that the change in heat capacity is primarily due
to enhanced low-frequency modes within the shear band region.
