Van der Waals materials resemble a layered deck of cards: they are made of individual sheets which are weakly bonded to their neighbors. In this last decade it was discovered that these individual sheets can be peeled off to produce a one-atom thick material. This highly surprising discovery was first made with graphite to isolate single atomic layers called graphene. Since then this technique has been applied to a range of materials to isolate new forms of 2-dimensional layered crystals. When isolated in this way, it has been found that the thin layered sheets take on new properties which can be useful for a wide range of electronics applications. At the forefront of this research is the creation of van der Waals heterostructures, which are made by combining thin layers from different materials to create entirely new structures with novel functionality. This research project explores how the properties of the combined structure can be altered by "twisting" the structure, i.e. by changing the rotational alignment between adjacently stacked layers. Twisting one layer with respect to another can drastically affect the coupling between the two layers, resulting in widely different electronic properties for the combined structure. In this way the properties of the new electronic material can be tuned for different purposes such as for the study of exotic quantum phenomena or to obtain novel quantum nanodevices with new electronic and optical properties. This project will be accomplished as part of a broadly integrated program aimed at building a collaborative and open scientific community, mentoring the next generation of scientists, and communicating physics to industry leaders and the general public.
The stacking of 2d crystalline layers to form van der Waals heterostructures constitutes a new paradigm for creating designer electronic materials. The range of possible electronic phenomena is especially rich due to the sensitivity of interlayer coupling and Coulomb interactions to the rotational alignment between layers, or twist angle. The research objective of this project is to understand the interlayer physics that determine the properties of twisted van der Waals heterostructures and to build upon this understanding to engineer novel quantum circuits. The proposed research objective will be achieved through the nanofabrication and transport measurement of van der Waals heterostructures made from stacking atomically-thin layers of graphene and hexagonal boron nitride. The success of this project will result in an understanding of the effect of interactions within van der Waals heterostructures due to interlayer coupling and electron-electron interactions. Moreover, electron-electron interactions are expected to give rise to new highly-correlated ground states and novel edge state configurations such as the fractional quantum spin Hall effect. This project will probe these novel many-body states in twisted van der Waals heterostructures and explore their potential for realizing building blocks for future topological-protected quantum circuits. This research may also result in new quantum coherent electronic devices, and will be of importance in assessing the potential of van der Waals heterostructures to become a component in future nanoelectronics and quantum information technologies.
