Understanding Electronic Inhomogeneity in 2D Layered Materials and Structures via Cryogenic STEM

Two-dimensional quantum materials exhibit unique phenomena and functionalities beyond classical physics. Constructing hetero- and twisted structures from them has emerged as a promising method to induce distinctive local lattice reconstructions and thus induce exotic quantum effects. Critical to this research is studying the spatial inhomogeneity of these materials to finely tune their quantum states. Advances in cryogenic scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) with enhanced stage stability have significantly enabled this research. In this talk, I will present our ongoing research using atomic-scale cryogenic STEM and monochromated EELS to investigate lattice-electronic structure coupling in several representative 2D van der Waals structures for magnetic storage and spintronic applications. Key examples include the discovery of layer-number-dependent phase transitions in CrCl₃ during cooling, the elucidation of complex local symmetry breaking in the long-wavelength charge density wave in EuAl₄, and the mapping of local excitons in moiré-structured MoTe₂. These studies demonstrate that the electronic and magnetic properties of 2D materials can be tuned by manipulating the layer number, introducing lattice displacements, or creating moiré structures. These studies also highlight the power of combining high-resolution cryogenic STEM imaging and spectroscopy for studying quantum materials in general.<br/><br/>This work was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Microscopy was performed as part of a user proposal at the Center for Nanophase Materials Sciences (CNMS), which is a US DOE Office of Science User Facility at Oak Ridge National Laboratory (ORNL).