Painting potential landscapes on an atomically thin canvas

Abstract: Atomically thin van der Waals crystals like graphene and transition metal dichalcogenides allow for the creation of arbitrary, atomically precise heterostructures simply by stacking disparate monolayers without the constraints of covalent bonding or epitaxy. While these are commonly described as nanoscale LEGO blocks, many intriguing phenomena have been discovered in the recent past that go beyond this simple analogy.

In this talk, I will discuss two stories from our joint experimental and theoretical work focusing on the prototypical 2D semiconductor interface of monolayer WS2 and WSe2. In part one, we use ultrafast electron diffraction to uncover the role of layer-hybridized electronic states as a powerful route to control ultrafast energy transport across atomic junctions. In part two, we use electron energy loss spectroscopy to directly visualize the nanoscale real space localization of excitonic states within the moiré unit cell of WS2 and WSe2, opening up the possibility for on-demand engineering of excitonic superlattices with nanometer precision. These works are a result of fruitful collaborations with colleagues at various institutions including SLAC National Laboratory, Stanford, Molecular Foundry, UC Berkeley, Purdue University and NIMS Tsukuba.

Bio: Archana Raja completed her undergraduate degree in Chemistry at the Indian Institute of Technology in Bombay and obtained her PhD in Chemical Physics from Columbia University. After spending a year as a postdoc in the Applied Physics department at Stanford University, she was awarded the Heising-Simons postdoctoral fellowship and joined the Kavli Energy and Nanoscience Institute at UC Berkeley. In July 2019, she was awarded the Early Career Lab Directed Research and Development Award at Lawrence Berkeley National Laboratory, where she is currently a Staff Scientist at the Imaging and Manipulation of Nanostructures Facility of the Molecular Foundry. She is also the recipient of the Institute Silver Medal at the Indian Institute of Technology in Bombay and the Blanche R. and David Kasindorf Fellowship in Physical Chemistry at Columbia University.

Zoom Link: https://stanford.zoom.us/j/92153920201?pwd=YW5PV1kxek9Cd2xuY0xwWU9zNWdWUT09

Zoom Password: 257509