Living Metals

Using synchrotron x-ray microbeams, a research team from the Max Planck Institute for Metals Research in Stuttgart and the ESRF has been able to observe for the first time that the microscopic structure of a crystalline material fluctuates in time. The results are published today in Science Express with the title: Scaling in the Time Domain: Universal Dynamics of Order Fluctuations in Fe3Al.

The research team investigated a metal alloy, composed of iron and aluminium. When the structure of such a crystalline material changes upon heating, x-ray scientists can observe this by means of a diffraction experiment: One class of interference peaks associated with the low-temperature structure disappears, while another class of x-ray peaks belonging to the new structure may emerge. For a fixed temperature, however, the x-ray diffraction pattern has hitherto always been found to be static according to standard textbook wisdom.

The novel observation is now that this x-ray diffraction pattern shows fluctuations in time when the beam is focused to a very small size of a few micrometers. This gives clearcut evidence that temporal structural fluctuations on an atomic scale are present in the crystal at fixed temperature. By using a very small beam, the number of the temporal fluctuations “seen” by the x-ray beam is so small that these fluctuations now become visible as x-ray intensity fluctuations.

This discovery helps to shed light on a very fundamental aspect in the theory of condensed matter, namely to understand and predict how a given material reacts upon external perturbations like changes in temperature, pressure, magnetic or electric fields. Solid state theorists predicted a long time ago that the way that a material responds to these changes of external conditions is governed by these temporal fluctuations in the system. For the iron-aluminium alloy that was studied, these experimental results can be used for a test of the existence of universal, materials-independent laws in the dynamics of microscopic fluctuations.