Coherent Quantum Dynamics of Indirect Excitons and Valley Pseudospins in Atomically Thin Semiconductor Heterostructures

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Non-Technical Abstract: Scientists have been exploring methods of controlling material properties by confining electron motions to lower dimensions for nearly four decades. These quantum materials have led to improved light emitting devices, such as light emitting diodes and lasers, and information processing and communication devices (e.g. computers and cell phones) that have transformed our lives. It is now possible to create a sheet of matter just a single atom thick. These ultrathin materials, known as monolayer materials, represent the ultimate thickness limit of two dimensional (2D) materials. This project asks how we may create better and more complex 2D materials by stacking two or several of these ultrathin sheets together. Ultrafast laser light pulses, akin to a camera with very fast shutter speed, are used to probe the stacked structures and capture the motion of electrons in the materials. Ultimately, these studies teach us how to control the properties of materials by manipulating individual electrons. New insights on these novel materials guide the development of new energy harvesting and information processing technologies. This project also provides valuable training opportunities for young researchers in areas critical to sustaining the nation's technological competitiveness. Technical Abstract: An emerging class of heterostructures consisting of atomically thin layers represents two-dimensional quantum materials in the ultimate thickness limit. By stacking two monolayer transition metal dichalcogenides (TMD), a semiconducting vertical heterostructure (VHS) is formed. Because of the type II band alignment typically found in TMD VHSs, electrons and holes rapidly transfer to different layers following optical excitation, leading to the formation of interlayer excitons. The research group investigates coherent quantum dynamics associated with interlayer excitons and valley pseudospins in a TMD VHS using a powerful nonlinear spectroscopy tool known as two-dimensional Fourier transform spectroscopy. Understanding the coherent properties of these pseudospins (i.e., excitons and valley index) guides the development of quantum devices based on these novel two-dimensional materials, enabling transformative impacts on information communication and processing technologies. This project also provides valuable training opportunities for young researchers as future workforce, placing the U.S. in a globally competitive position in the emerging market of quantum technology.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.