Imaging and controlling moire interactions in two-dimensional semiconductor heterostructures

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Two-dimensional (2D) materials are a single or few atoms thick. These ultra-thin materials exhibit a host of new electronic and other effects that have applications to new technologies, such as high speed computing, solar energy harvesting, and quantum-based technologies. Over the past decade, many 2D materials have been discovered, including 2D metals, semiconductors, and magnets. Furthermore, these 2D materials can be stacked together to realize properties that are enabled by the interactions between layers. These new properties enable electronic and optical devices, like transistors, solar cells and lasers. This research is focused on investigating multi-layer 2D material samples that use these interlayer interactions to realize new electronic and optical properties. In particular, by combining two different 2D semiconductors, the research team will explore states with trapped electrons. These trapped electrons can act as quantum light sources, which would help enable quantum communication devices that are secure against cyber-attacks. This research aligns with the NSF Big Idea of the Quantum Leap: Leading the Next Quantum Revolution by developing material systems that have the potential to enable these new quantum information technologies. Furthermore, the project strengthens the STEM workforce both directly and indirectly by training and mentoring graduate, undergraduate, and high school students through the proposed research, and by encouraging interest in STEM at the high school level in southern Arizona.The stacking of 2D materials in a vertical heterostructure leads to the formation of a long wavelength moiré pattern due to the lattice mismatch and relative orientation between the layers. This moiré pattern modulates the electronic and optical properties of the heterostructure leading to the confinement of electrons in one layer and holes in the other layer. These confined indirect excitons are known to serve as resources for quantum information science, and the PI will investigate how the novel physics of moiré confined excitons in 2D semiconductor heterostructures can be exploited to realize quantum devices with new functionalities. This project is focused on 2D semiconducting transition metal dichalcogenide heterostructures consisting of MoSe2 and WSe2 which form a type-II heterojunction. The research in this project advances knowledge of quantum materials physics by developing a comprehensive understanding of the role of twist angle and interlayer interactions in transition metal dichalcogenide heterostructures. In particular, the research has three aims: (1) Image the moiré potential in MoSe2/WSe2 heterostructures using scanning tunneling microscopy, (2) Directly measure spatially modulated moiré exciton emission using low-temperature scanning near field optical microscopy and (3) Control moiré interlayer excitons in 2D heterostructures. Lastly, modifying the interaction between layers and the potential landscape, allows for the tuning of the interlayer bandgap, the charging of trapped moiré excitons and the condensation of interlayer excitons in the moiré potential.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.