Collaborative Research: Combined transport and scanning probe study of twisted van der Waals devices

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Nontechnical AbstractMany semiconductor devices rely on creating heterostructures consisting of multiple layers to enable their desired functionality. Traditional semiconductor heterostructures are limited in the choice of materials that can be utilized because of requirements of lattice matching between the different layers. However, atomically thin materials have the ability to overcome this limitation through the creation of van der Waals heterostructures realized in a layer-by-layer stacking approach. This will allow a much wider range of electronic properties to be created in these heterostructures. Furthermore, they have an additional degree of freedom which is the twist angle between different layers, which gives rise to a long wavelength moiré pattern between the layers. This moiré pattern modulates the electronic properties, and can give rise to correlated states such as superconductivity or magnetism. In this project, we will use semiconducting transitional metal dichalcogenides of the form MX2 where M is a transition metal, and X is a chalcogen to create novel Boolean logic devices where the twist angle between layers controls the electronic properties. The proposed project will develop new fabrication techniques, characterize the novel electronic properties, and then implement logic devices based on these newly developed heterostructures. The proposed program will create new educational and research opportunities at University of Arizona and The University of Texas at Austin by fostering the growth of the interdisciplinary area of quantum materials and devices. In particular, the proposed research aligns with the NSF Big Idea of Quantum Leap: Leading the Next Quantum Revolution by developing material systems and devices that have the potential to enable new quantum technologies. This proposed research prog¬ram will strongly emphasize the training of graduate and undergraduate students, thus preparing them for industrial or academic careers.Technical AbstractThis collaborative proposal will engineer and characterize van der Waals heterostructure devices with flat bands through heterostructure design, layer-by-layer fabrication, scanning probe microscopy, and electrical transport measurements. The project will be focused on homobilayer heterostructures of two-dimensional semiconducting transition metal dichalcogenides with controlled twist angle between the layers. Due to the twist angle between adjacent layers, a long wavelength moiré pattern develops which modifies the electronic properties of the heterostructure and can lead to an energy-momentum dispersion that is flat. These flat bands have a large density of states and small bandwidth such that interaction effects will dominate over their kinetic energy. In this regime, the electronic effects become highly correlated and we will exploit these properties for the creation of novel devices. In particular, we will accomplish the following three aims: (1) Development and characterization of gate tunable TMD homobilayer and trilayer heterostructures, (2) Creation of novel correlated states through electrostatic gating, twist and strain control, and (3) Realization of Josephson junction field-effect transistors for Boolean logic applications. Statement of Merit ReviewThis 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.