An-Ping Li leads the Scanning Tunneling Microscopy Group and the Heterogeneities in Quantum Materials theme at the Center for Nanophase Materials Sciences, Oak Ridge National Laboratory. His research focuses on understanding and controlling the atomic structure and its correlation with electronic, magnetic, and transport properties in quantum materials through the development of advanced scanning tunneling microscopy (STM) techniques. His group has established unique capabilities, including a dilution refrigerator vector-magnet STM, a spin-polarized four-probe STM, and a scanning NV microscope. These tools have enabled major discoveries such as the identification of skyrmions in van der Waals magnets, direct evidence of spin–momentum locking in topological materials via spin chemical potential measurements, observation of single-vacancy-based nonvolatile resistive switching (NVRS), and the demonstration of single-molecule telegraphy across surfaces.
Presentation Title:
Probing Topologically Protected Quantum States with Scanning Tunneling Microscopy
Presentation Abstract:
Topological quantum materials (TQMs) host electronic states that are protected by band topology, giving rise to novel phases such as topological insulators and superconductors. Their properties can be tuned by magnetism, thickness, or external fields, enabling a rich landscape of 2D and 3D quantum phenomena. Many of these exotic states—such as gapped Dirac surface states, dissipationless edge conduction, and emergent quasiparticles—are expressed at the material surface, where they can be directly probed. Scanning tunneling microscopy (STM) provides atomic-scale access to structural, electronic, and magnetic properties, making it uniquely suited to investigate these phenomena. Using STM and multi-probe STM, we demonstrate how local spectroscopy and transport measurements reveal key signatures of topological states, from exchange gaps and thickness-dependent topology to spin-momentum locking and Majorana zero modes. These results underscore the central role of STM in advancing our understanding and control of quantum matter.