Surface Modalities of Stacked 2D Heterostructured Topological Materials

Topological materials present new challenges in terms of characterization, in particular how to minimize surface and sample damage while imaging and analyzing surfaces at the direct native level. Therefore, novel approaches are needed in order to corelate materials properties with surface topology. We have adapted LEEM multi-modal techniques such as Low Energy Electron Diffraction (LEEP), Photoemission Electron Microscopy (PEEM) and in-situ ARPES with high temperature annealing to study individual surface modalities. We have examined various topological materials in the form of bulk 2D heterostructures, specifically artificially constructed metasurfaces with unique order parameters (spin, lattice, localized charge and collective excitations (such as plasmons)).<br/><br/>It is possible to form, via controlled growth, systems with heterointerfaces in bulk materials. We will present the structure analysis of a novel synthesized material Ba6Nb11S28 along with key physical properties. This material naturally realizes vdW coupled heterointerfaces between transition metal dichalcogenide (TMD) monolayers (hexagonal NbS2, H-NbS2) and insulating spacers Ba3NbS5. TEM diffraction taken along the c-axis shows that the hexagonal spacer and TMD layers are commensurate. The electronic band structure can be understood as that resulting from superimposing a periodic potential defined by Ba3NbS5 onto monolayer H-NbS2. This is similar to the mechanism which yields flat bands and strongly correlated physics in twisted-bilayer graphene and TMD heterostructures. LEEM techniques and Low Voltage electron microscopy has been used to characterize grown materials with high resolution at low beam voltages to directly confirm structural layers, ordering and surface diffraction and relate them to metrics of possible topolgical material performance.<br/><br/><b>Acknowledgement</b><br/>This work was supported by the STC Center for Integrated Quantum Materials, NSF Grant No. DMR-1231319. This work was supported by an MRI grant from the National Science Foundation DMR-1828237 “The acquisition of a Low Energy Electron Microscope for Nanoscience research”<br/><br/><b>References</b><br/>[1] Devarakonda A, Inoue H, Fang S, Ozsoy-Keskinbora C, Suzuki T, Kriener M, Fu L, Kaxiras E, Bell DC, Checkelsky J. G. <i>Science</i> Oct 9;370(6513):231-236 (2020).<br/>[2] Bell D, Erdman N. Low Voltage Electron Microscopy. Bell D, Erdman N, editors. Chichester, UK: John Wiley & Sons, Ltd; (2012)