Condensed Matter Seminar: Ultrafast electron diffranction studis of materials at extreme conditions

In this presentation, we will review recent progress in characterizing the ultrafast excitation and the transformations of materials using Ultrafast Electron Diffraction (UED) at mega-electron volts energies. These experiments resolve material dynamics at ultra-fast temporal (1 ps) and atomic spatial (1 Å) resolutions. Initially motivated by the need to understand the material responses to the harsh environments produced by fusion plasmas, that emit intense radiation by X-rays, neutrons and plasma charged particles, we successfully visualized heterogeneous and homogeneous melting and plasticity regimes [1-4]. Importantly, our data quantify the dependencies on nucleation seeds and have determined dislocation nucleation and transport properties that constitute the underlying defect kinetics and incipient plasticity. Comparisons with modeling that include two-temperature Molecular Dynamics (MD) simulations reveal the crucial role of the choice of the inter-atomic potentials to describe the material state in extreme conditions. The successes of these studies have motivated us to expand this research area at SLAC; the combination of structural data from UED ultrafast laser-excited materials with accelerator and laser-based THz [5, 6] and free electron laser measurements is now providing new insight into questions ranging from electrical and thermal conductivity to the microphysics of radiation-damaged materials.

References:

[1] M. Mo et al., Science (2018).

[2] M. Mo et al., Science Advances (2019).

[3] M. Mo et al., Nature Comm. (2022).

[4] M. Mo et al., Science Advances (2024).

[5] Z. Chen et al, Nature Comm. (2021).

[6] B. Ofori Okai et al., Phys. Plasma (2024).