CAREER: Real-Space Topological Control of Excitons in Twisted 2D Semiconductors

Non-technical Abstract: Topology, which is the study of geometric properties, has profoundly reshaped modern physics and materials science. For example, in some materials topology can confine a class of quasiparticles called excitons, which are sensitive to external perturbations such as strain and electric field. The central goal of this project is to determine how topology affects exciton confinement in low dimensional quantum materials. The insights gained from this work are expected to have far-reaching implications, including the development of excitonic devices for low-power computing. On the educational front, this project integrates creative and inclusive outreach programs aimed at expanding access to materials science and quantum concepts among K-12 students. Programs such as Materials Your Mind (middle school) and Let’s Code Materials (high school) use visual arts and coding-based projects to introduce core ideas of topology, lattices, and excitons in an engaging and intuitive manner. These activities are sustained and scaled through partnerships with existing outreach platforms within Arizona State University and support increased undergraduate recruitment into materials science and engineering. Technical Abstract: The ultimate goal of this CAREER project is to uncover how short- (<10 nm) and long-range (>10 nm) topological textures in real space modulate exciton confinement and character in twisted heterostructures, with a focus on homobilayer transition metal dichalcogenides such as tungsten diselenide. These materials exhibit rich topological textures on the moiré scale (<10 nm) with sensitivity to both strain-induced lattice buckling (>10 nm) and out-of-plane electric fields and directly affecting the excitonic states. The central hypothesis is that real-space topological heterogeneity at multiple length scales controls the localization, type, and dynamics of excitonic states, including their transformation between delocalized and localized forms. To investigate this hypothesis, this CAREER project uses low-loss scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) to conduct the real-space excitonic mapping at low temperatures with strain variations and external electric field, organized into two research thrusts. Thrust 1 investigates how in-plane strain gradients modulate short- and long-range real-space topology and alter excitonic confinement, energy levels, and symmetry by identifying strain regimes that induce topological transformations, change winding numbers, and trigger exciton delocalization-to-localization transitions. Thrust 2 explores how out-of-plane electric fields reconfigure topological textures and induce novel exciton complexes and confinement geometries. Specifically, Thrust 2 develops in-situ cryogenic-STEM-EELS under electrical bias using Micro-Electro-Mechanical Systems-integrated devices. Overall, this project establishes real-space topology as a tunable and robust control parameter for exciton confinement, validate cryogenic-STEM-EELS as a powerful and generalizable tool for imaging quantum states, and provide predictive design principles for engineering excitonic devices and quantum materials. Collectively, these outcomes open new frontiers in condensed matter physics, nanophotonics, and quantum information science. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2542499 | Program: 01003031DB NSF RESEARCH & RELATED ACTIVIT,01002930DB NSF RESEARCH & RELATED ACTIVIT,01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Sandhya Susarla | Institution: Arizona State University, SCOTTSDALE, AZ | Award Amount: $419,790 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2542499 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2542499.html