"Nanoscale Molecular and Ionic Di1usion in Quantum Materials"
The interaction of quantum materials with diffusion-driven ions or molecules gives rise to a range of intriguing phenomena, including surface, subsurface, and interface modifications, as well as changes in electronic, optical, and chemical properties. However, understanding the action of molecular and ionic diffusion at the nanoscale presents a formidable challenge in unraveling the fundamental mechanisms involved. In this talk, I will present recent results that provide quantitative insights into the role of diffusion-driven ionic or molecular interactions in altering the complex dielectric function of two classes of quantum materials: correlated oxides and van der Waals (vdW) crystals at the nanoscale. Our recent works reveal how an applied field perturbs ion diffusion at the nanoscale in correlated oxides such as rare-earth nickelates (RNiO3 where R =
rare-earth element), leading to ordered reconfigurable phases. This reconfigurability enables the design of robust artificial synapses and opens new frontiers for fundamental understanding of memory, learning, and information retention for brain-inspired information processing. The interaction of vdW crystals with diffusing oxygen and water molecules in an ambient environment leads to enhanced chemical reactivity of their extraordinarily high surface areas. Using nano- optical correlative imaging and spectroscopy, I will present recent results revealing exotic interfacial vdW interactions and the formation of oxidized molecular species in 2D heterostructures and thin flakes of phosphorus allotropes (black and violet phosphorus). I will conclude by briefly presenting a recent exciting idea we are exploring on the connection between diffusion and topology, focusing on the role of path-connectivity as a topological invariant that determines whether a diffusing particle can reach a target receptor within a confined region.
