Available on-demand - *S.NM12.03.02
Probing Order and Disorder in Quantum Materials Using Scanning Transmission Electron Microscopy
Cornell University1,Kavli Institute at Cornell2
Coupling between charge, spin, lattice, or orbital degrees of freedom gives rise to remarkable phenomena such as colossal magnetoresistance, metal–insulator transitions and superconductivity. Many aspects of these competing interactions, however, remain elusive. Traditional bulk measurements of phases transitions, which average the material’s response over large length scales, can inferred the presences of spatial inhomogeneity. Understanding their character, however, requires local probes. Direct, real-space measurements of the onset of emerging order are key to understanding the diverse properties of complex electronic materials.
Today, atomic-resolution imaging is routinely achieved by aberration-corrected scanning transmission electron microscopy (STEM). Coupled with spectroscopy STEM provides direct information about the local structure and chemistry of thin films and heterostructures. In this talk, I will first discuss our results on two classes of superconducting materials, the layered perovskite ruthenates and the recently reported infinite-layer nickelates , with particular focus on the microscopic structure, strain and the role of defects in these thin film superconductors. Going beyond room temperature STEM, cryogenic sample cooling promises direct access to low temperature phases. While limitations in hardware currently hamper STEM measurements of ruthenates and nickelates in their superconducting states, high-precision cryogenic STEM near liquid nitrogen temperature has been demonstrated [2, 3]. These new capabilities have paved a path to visualize subtle lattice and electronic orders in emergent low temperature phases as I will show in the second part of the talk. Focus will be on the lattice behavior of charge-ordered manganites, where direct imaging can discriminate between multiple structure models, and mapping over larger length scales shows phase coexistence and nanoscale inhomogenities.
 D. Li, K. Lee, B. Y. Wang, M. Osada, S. Crossley, H. R. Lee, Y. Cui, Y. Hikita, H. Y. Hwang, Nature 572, 624 (2019).
 B. H. Savitzky et al., Ultramicroscopy 191, 56 (2018).
 I. El Baggari, B. H. Savitzky, A. S. Admasu, J. Kim, S.-W. Cheong, R. Hovden, L. F. Kourkoutis, Proc. Natl. Acad. Sci. 115, 1445 (2018).
 Research performed in collaboration with Ismail El Baggari, Berit H. Goodge, David J. Baek, Michael J. Zachman and the groups of Harold Y. Hwang (Stanford), Darrell G. Schlom (Cornell), Kyle M. Shen (Cornell) and Beth Nowadnick (New Jersey Institute of Technology). This work was supported by the DoD, AFOSR (FA 9550-16-1-0305), NSF (DMR-1539918, DMR-1429155, DMR-1719875), and the Packard Foundation.