In most cases the functionality of materials is related to macroscopic properties and their changes. Macroscopic properties the result from microscopic properties as well as from order and disorder on the nanometer to micrometer scale. This is very well known for magnetic materials, for which local magnetic moments, their coupling on an atomic scale and the domain pattern, determine their macroscopic magnetization. There is increasing evidence, that domain formation is a much more general phenomenon and that some of the most spectacular material properties like the colossal magnetoresistance observed in manganite samples, are caused by an interplay of local phase transitions and changes of domain pattern. In particular systems with complex energy landscapes that are in the focus of the proposed VI tend to form several almost degenerate phases which may coexist in a domain pattern on the several nm to µm length scale. Understanding material’s functionalities hence needs studies of the local electronic structure (P7, P9) as well as the domain pattern.
In this project domain patterns of complex materials and their changes with temperature and under the influence of external fields shall be studied. The main tool will be coherent X-ray scattering techniques, which are suited to image the domain pattern as well as to directly observe the domain dynamics in real time. The group of Grübel has a broad experience in coherent X-ray scattering techniques. It is operating a dedicated beam line for coherent diffraction techniques at PETRA III and carries out complementary experiments at the free-electron-laser sources FLASH and LCLS. Preliminary experiments from phase separation in a model system at the ESRF in collaboration with Schüßler-Langeheine and Goedkoop have shown the feasibility to study domain dynamics in such a correlated electron system in the medium hard X-ray range (5-20keV) via its coupling to structural degrees of freedom.
The goal of the project is to determine the pattern and dynamics of phase separation in a correlated electron system using diffraction of coherent X-rays and relate length and time scales of the dynamics.
A close collaboration with Schüßler-Langeheine (HZB) (P7) and Goedkoop will be established. The project is complementary to work with coherent soft X-rays probing electronic degrees of freedom but for a small part of the momentum space (P5, P6). The photoemission experiments (P9, mainly probing the averaged electronic structure) act as bridge between local and larger-scale probes. There is methodological synergy with P1, P4, P5, P6, P6.