Innovative Electron Probe Methods for van der Waals Heterostructures Topological Materials Discovery*

New Topological Insulators (TI) quantum materials with interesting/useful properties has caused great excitement and promises to transform device design and computation.   Remarkably, some of the quantum phenomena displayed by these materials now persists at room temperature, opening the way for usable devices.   

We present results from studies of TI's such as  Ba₆Nb₁₁S₂₈ . This material naturally realizes vdW coupled heterointerfaces between transition metal dichalcogenide (TMD) monolayers (hexagonal NbS₂, H-NbS₂) and insulating spacers Ba₃NbS₅  Low Energy Electron Diffraction (LEED) 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 correlated physics in twisted-bilayer graphene and TMD heterostructures and is one of the key advances in the prediction of band structure and properties.  We examine these materials with direct electron probe /photoemission methods Low/Photoemission Energy Electron Microoscopy (L/PEEM)  and ARPES. LEEM is an extremly low energy electon probe method that allows fine surface(S) probing down to several layers.   We show that new approaches to probing methods can show that behavior is a consequence of the underlying symmetry properties of the multi-layer system, lattice such as in the spin-orbit coupled ferromagnetic state. 

The analysis of TI quantum materials presents new challenges on how to minimize surface and sample damage, new approaches to corelate materials properties with the pseudo 2D structure , we present some of our multi-modal and electron and photoemission probe techniques approach in this presentation.