PARADIM Highlight #95—In-House Research (2025)
Lena F. Kourkoutis (Cornell), Ismael El Baggari (Harvard), Berit H. Goodge (MPI-CPfS), and Sang-Wook Cheong (Rutgers)
Strong interactions between electrons in quantum materials give rise to useful and exotic properties such as superconductivity and charge order. The quantum states are shaped by the presence of “topological” defects, which disrupt order on the nanoscale and alter their functional macroscopic properties. Understanding the behavior of these defects is thus crucial to controlling and harnessing strongly correlated materials but measuring them and their dynamics in response to applied stimuli is a significant experimental challenge.
Figure 1: (Left) Atomic-resolution imaging and atomic displacement, arrows showing direction & amplitude, and orientation map of the displacement stripes at 198 K. (Right) Charge order defects and motion at low temperatures as indicated, while tracking the position of a topological defect (red T marker) and its trajectory through the material (thin red line).
Leveraging PARADIM’s unique cryogenic scanning transmission electron microscopy capabilities and expertise, members of the In-House Research Team performed cutting-edge atomic resolution electron microscopy measurements to track the motion of topological defects as a charge ordered phase melts in an oxide material (Bi1−𝑥Sr𝑥−𝑦Ca𝑦MnO3). To achieve this, the team used an advanced cryogenic sample holder to track a nanoscale region of interest while simultaneously measuring picometer-scale atomic displacements associated with charge order and controlling the sample temperature to drive the melting transition. These experiments revealed subtle reconfigurations within the network of topological defects, which are critical to understanding the responses of correlated electronic phases.
This work demonstrates the capability to track the structure of a quantum material at atomic resolution over a consistent region of interest through a low-temperature phase transition with electron microscopy for the first time. This experimental breakthrough builds on the innovations in cryogenic scanning transmission electron microscopy, in particular in high-resolution and variable cryogenic temperature imaging, developed by the in-house PARADIM electron microscopy research team. This imaging capability was used to measure subtle picometer scale periodic lattice displacements associated with charge order in a manganite material, to reveal the presence of networks of topological defects driving incommensuration of the charge order with the atomic lattice, and track the dynamic behavior of these defects in response to temperature changes as the charge order melted.
Charge order is widely present in the phase diagrams of quantum materials, competing with superconducting and magnetic phases. Incommensurate charge order, with a distinct periodicity from that of the underlying lattice, exhibits unique couplings with these competing phases and forms in many systems from networks of topological defects imparting significant nanoscale inhomogeneity. While the charge ordered ground state is fairly well understood and scattering measurements have revealed associated ensemble average structures, the nanoscale evolution of incommensurate charge order and the associated topological defects is poorly understood. This work directly reveals the complex structural changes and nanoscale reconfigurations undergone through the course of electronic phase transitions, key to understanding the formation, evolution, and destruction of order in quantum materials, with relevance beyond charge order in the manganates to e.g. pair density wave states and critical behavior in superconductors.
This work was made possible by PARADIM’s cutting edge cryogenic electron microscopy facility, which makes the unique combination of cryogenic temperature control and atomic resolution imaging demonstrated in this work available through its user facility.
Noah Schnitzer, Berit H. Goodge, Gregory Powers, Jaewook Kim, Sang-Wook Cheong, Ismail El Baggari, Lena F. Kourkoutis, N. “Atomic-Scale Tracking of Topological Defect Motion and Incommensurate Charge Order Melting,” Phys. Rev. X 15, 011007 (2025). doi:10.1103/PhysRevX.15.011007.
The authors thank David A. Muller, Suk Hyun Sung, Robert Hovden, and James L. Hart for helpful discussions, and Elisabeth Bianco for experimental support. This work was primarily supported by the National Science Foundation (NSF), Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM), under Cooperative Agreement No. DMR-2039380. The work at Rutgers University was supported by the Department of Energy under Grant No. DOE: DE-FG02-07ER46382. N. S. acknowledges support from the NSF GRFP under Award No. DGE-2139899. B. H. G. acknowledges support from Schmidt Science Fellows in partnership with the Rhodes Trust, and the Max Planck Society. The authors acknowledge the use of the Cornell Center for Materials Research shared instrumentation facility, a Helios FIB supported by NSF (DMR-1539918), and FEI Titan Themis 300 acquired through NSF-MRI-1429155, with additional support from Cornell University, the Weill Institute, and the Kavli Institute at Cornell. I E. acknowledges support by the Rowland Institute at Harvard.
Data Availability
The data sets generated and analyzed during the current study are available from the Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM) database .
