Finalist EPFL doctorate Award 2016 – Giulia Mancini

In disordered elastic media, elastic forces of different origin, e.g., chemical, magnetic, or electrostatic, provide the binding necessary to create order. Their interplay with disorder, of thermal or quantum origin, gives rise to universal behaviors which investigation has been mostly limited to the observation of frozen systems in static conditions. However, ordering and disordering phenomena are essentially dynamical. In this thesis, we demonstrate that it is now possible to determine the interplay between disorder and elastic forces, with a spatial resolution that allows distinguishing every microscopic constituent of the system, and with a temporal resolution in the time scale of their motions.

This has been possible through the implementation of a flexible Ultrafast Electron Diffraction set-up, which constitutes the first demonstration of far-field and small-angle diffraction with electrons in a single diffractometer (from few Å to a few tens of nm spatial resolution), with <250 femtoseconds (10¹⁵s) temporal resolution. In combination with Angular Cross-Correlation Analysis structure retrieval methods of the sample local order and symmetry, diffractive imaging has been carried out to study complex ordering/disordering phenomena in structure (supracrystal of alkanethiol-capped gold nanoparticles), charge (Charge Density Waves system 1T-TaS₂) and spin (Dzyaloshinkii-Moriya chiral insulator Cu₂OSeO₃) textures.