​Title: Spatial and temporal dynamics of excitons in van der Waals heterostructures

 

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. The theoretical part of these works utilized BerkeleyGW, and are a result of fruitful collaborations with colleagues at various institutions including UC Berkeley, SLAC National Laboratory, Stanford, Molecular Foundry, Purdue University and NIMS Tsukuba.

 

Bio: Dr Archana Raja is a Staff Scientist at Lawrence Berkeley National Laboratory. Her research group is based at the Imaging and Manipulation of Nanostructures Facility at the Molecular Foundry, a nanoscale science research center based at Berkeley Lab. She received her PhD in Chemical Physics from Columbia University. After spending a year as a postdoctoral scholar in the Applied Physics department at Stanford University, she joined the Kavli Energy and Nanoscience Institute at UC Berkeley as a Heising-Simons Junior Fellow. Her research focuses on manipulating potential landscapes in nanoscale quantum materials for transport of energy, charge, and information.