Low-temperature entropy in Cu-based shape-memory alloys and the boson peak

Abstract

We have measured the energy and entropy differences between $\ensuremath{\beta}$ and martensitic phases in Cu-Zn and Cu-Zn-Al shape-memory alloy systems which display martensitic transitions in a range of temperatures between 30 K and 130 K. We show that the entropy difference originates in the low-energy ${\mathrm{TA}}_{2}$ vibrational modes and displays the predicted features for a system showing the so-called boson peak, characteristic of structurally disordered solids. In the studied systems the boson peak is conveniently revealed by the ratio between the entropy difference and the Debye entropy.