A fluctuation-based characterization of athermal phase transitions: Application to shape memory alloys

We employ a fluctuation-based technique to investigate the athermal component associated with martensite phase transition, which is a prototype of temperature-driven structural transformation. Statistically, when the phase transition is purely athermal, we find that the temporal sequence of avalanches under constant drive is insensitive to the drive rate. We have used fluctuations in electrical resistivity or “noise” in nickel titanium shape memory alloys in three different forms: a thin film exhibiting well-defined transition temperatures, a highly disordered film, and a bulk wire of rectangular cross-section. Noise is studied in the realm of dynamic transition, viz., while the temperature is being ramped, which probes into the kinetics of the transformation at real time scales, and could probably stand out as a promising tool for material testing in various other systems, including nanoscale devices.