Imaging the Structural Evolution of Strongly Correlated Order in Oxides with Cryogenic Electron Ptychography and Variable Temperature Cryo-STEM

Quantum materials host rich phase diagrams characterized by the competition of electronic, magnetic, and lattice degrees of freedom. The small energy barriers between phases with disparate properties give rise to rich couplings and exotic behavior such as charge and pair density waves and colossal magnetoresistance, as well as nanoscale inhomogeneity including phase coexistence, domain structures, active defects and disorder. Studying the emergence of these nanoscale features and their significance to functional material properties requires high resolution characterization, while stabilizing ground states of interest and tracking the evolution of order parameters under applied stimuli necessitates <i>in situ</i> measurement. Here, we apply cryogenic scanning transmission electron microscopy (cryo-STEM) to characterize the emergence and destruction of strongly correlated electronic phases in complex oxides with sub-Angstrom resolution, and demonstrate two emerging cryo-STEM techniques. First, we apply variable temperature cryo-STEM imaging, enabled by <i>in situ</i> holder developments, to step through a low-temperature electronic phase transition in a charge-ordered manganite and reveal transient structures which reflect the coupling between the charge ordering and the lattice. Secondly, we leverage cryogenic multislice electron ptychography, made possible by high-speed, high-dynamic-range 4D-STEM detectors, to achieve deep-sub-Angstrom spatial resolution imaging with light-element sensitivity to probe the strain-mediated metal-insulator transitions in Ruddlesden-Popper ruthenate thin films.