Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and pressure-dependent electrical transport measurements have been made on single crystals of AuZn and Au_{0.52}Zn_{0.48} above and below their martensitic transition temperatures (T_M=64K and 45K, respectively). In each composition, elastic neutron scattering detects new commensurate Bragg peaks (modulation) appearing at Q = (1.33,0.67,0) at temperatures corresponding to each sample's T_M. Although the new Bragg peaks appear in a discontinuous manner in the Au_{0.52}Zn_{0.48} sample, they appear in a continuous manner in AuZn. Surprising us, the temperature dependence of the AuZn Bragg peak intensity and the specific-heat jump near the transition temperature are in favorable accord with a mean-field approximation. A Landau-theory-based fit to the pressure dependence of the transition temperature suggests the presence of a critical endpoint in the AuZn phase diagram located at T_M*=2.7K and p*=3.1GPa, with a quantum saturation temperature \theta_s=48.3 +/- 3.7K.
@article{arxiv.0808.1734,
title = {Observation of a continuous phase transition in a shape-memory alloy},
author = {J. C. Lashley and S. M. Shapiro and B. L. Winn and C. P. Opeil and M. E. Manley and A. Alatas and W. Ratcliff and T. Park and R. A. Fisher and B. Mihaila and P. Riseborough and E. K. H. Salje and J. L. Smith},
journal= {arXiv preprint arXiv:0808.1734},
year = {2009}
}