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About the Coherent X-ray Science Group

Overview

Our group is interested in understanding phenomena in strongly correlated materials. In these materials the interaction between the valence electrons can strongly influence the materials properties. They are interesting as their unique properties are of considerable utility for device physics, functional materials and fundamental condensed matter physics. Some of these materials exhibit a reconstructive structural phase transition (SPT) at some critical temperature that occurs on the femto-second time scale. There is still a great deal that is not known about the dynamics of this phenomenon as the ability to probe ultra-fast transitions remains largely inaccessible to conventional techniques. For example, electron microscopes are able to resolve atomic scale features of sufficiently thin materials but have poor time resolution. Conversely, femto-second laser systems (excluding hard X-ray systems) have poor spatial resolution and cannot resolve atomic structural changes.

To study these materials, our group makes use of femto-second coherent X-ray diffraction imaging to study ultra-fast SPT's in nanoscale materials. This process became possible with the advent of the X-ray Free Electron Laser (XFEL) synchrotron radiation facility. Bragg coherent X-ray diffraction imaging (BCXDI) is a powerful lens-less imaging technique for probing crystalline materials with sub-nanometre sensitivity. When BCXDI imaging is performed using the femto-second timing of an XFEL, we can obtain three-dimensional images of nanoscale structures with femto-second temporal resolution and nanometre spatial resolution. As a result, we are able to address the fundamental problem of how to determine atomic motions during a SPT in solid-phase materials.

Our group is also engaged in large scale supercomputer simulations of structural phase transitions. We make use of the Iridis high-performance computing facility to perform ab-initio molecular dynamics (MD) simulations of structural phase transitions under various conditions. Simulations of the ultra-fast SPT allow us to bridge XFEL experiments to current theory and to make predictions as to how the behaviour of a material changes under various conditions. This might relate to a change in the immediate environment of the material or the materials use in a heterostructure device setting.

Acknowledgements

Our research facilities are generously furnished in part by a prestigious JSPS Grant-In-Aid (Kakenhi) research grant award and a Royal Society Research Grant award. We graciously acknowledge research funding support from the following bodies: