Optical and AFM Spectroscopy Studies of the Crystal Structure of Quasi-2D Van der Waals Crystals

Quantum materials are sensitive to external fields. Recently, our group has developed methods for combining scanning tunneling microscopy/spectroscopy (STM/STS) with in situ uniaxial strain and in-plane electric fields for tuning the properties of quantum materials. Precise sample alignment along the crystallographic axes is essential when tuning large fields (strain/electric) to probe correlated states. In this talk, we present an ambient and accessible method for characterizing and aligning quasi-2D van der Waals crystals such as Bi₂Sr₂CaCu₂O_8+δ (BSCCO), NbSe₂, and other transition metal dichalcogenides (TMDCs)​ using polarization dependent optical reflectance spectroscopy and atomic force microscopy (AFM). Optical contrast and AFM surface morphology data enable identification of crystal axes and local polytype domains and assessment of pre-strain effects. Together, these techniques provide a simple, effective, and non-destructive approach for evaluating structural properties and alignment of layered superconductors under ambient conditions.