A fluctuation-based probe to criticality in structural transitions

Many natural phenomena, extending from biology to material science, involve slowly driven dissipative systems that are far from thermal equilibrium, triggered only by a slowly varying external field and to which the systems respond through scale-free avalanches in physical observables. In spite of decades of research, experiments are inconclusive whether these systems self organize to the critical state over a broad range of external field, or if there exists a unique critical point that is smudged by a wide critical zone. Here, through the higher order statistics of time dependent avalanches, or noise, in electrical resistivity during temperature-driven martensite transformation in thin nickel-titanium films, we demonstrate for the first time, the existence of a singular `global instability' or divergence of the correlation length as a function of temperature. These results not only establish a mapping of non-equilibrium first order phase transition and equilibrium critical phenomena, but perhaps also call for a re-evaluation of many existing experimental claims of self-organized criticality. References: 1. U. Chandni et.al, Appl. Phys. Lett. 92, 112110 (2008). 2. U. Chandni et. al, arxiv:0811.0102 (2008).