Quantum Fluctuation of the Order Parameter in a Structural Phase Transition*

Using a variety of microscopic and bulk-thermodynamic probes (e.g., elastic neutron scattering, inelastic x-ray scattering, specific heat, and pressure-dependent electrical transport), we provide evidence for the presence of a continuous martensitic transition in the binary AuZn system. In Au$_{0.52}$Zn$_{0.48}$ and AuZn, elastic neutron scattering detects new commensurate Bragg peaks (modulation) appearing at $Q$ = (1.33, 0.67, 0) at temperatures corresponding to each sample's martensitic transition temperature, $T_{M}$. The pressure dependence of the transition in each alloy, shows a low-temperature saturation of the order parameter (strain-shuffle) that leads to highly non-linear phase boundaries in temperature-pressure space and to superconductivity in the case of Au$_{0.52}$Zn$_{0.48}$.