Imaging correlations and charge order in transition metal dichalcogenide moiré systems

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Non-technical abstract: The electronic properties of materials are governed by the arrangement of atoms and electrons within them. In most cases, this is fixed by the chemistry of the constituent atoms. However, recent advances in the ability to isolate atomically thin crystals and stack them on top of each other provide a route to engineer new synthetic materials. This project investigates how adding a small twist between adjacent layers can be used to control the positions and propagation of electrons. In particular, the rotational misalignment causes the electrons to interact especially strongly with each other, leading to new quantum electronic properties. The research uses a nanoscale sensor to image the resulting electron positions, study the new quantum states that form, and determine the degree to which they can be controlled. The predicted states may have applications in low-power electronics, fault-tolerant quantum computing, and high-density data storage. The project also trains undergraduate and graduate students for careers in quantum technology, fosters the involvement of underrepresented groups in science through summer internships, and inspires the next generation of researchers by developing and implementing outreach activities for high school students and local science festivals.Technical Abstract: Stacking van der Waals materials with similar lattice constants at small relative twist angle can generate exceptionally flat electronic bands that are susceptible to strong Coulomb interactions. This project aims to investigate the plethora of many-body phases that can be realized in twisted devices composed from semiconducting transition metal dichalcogenides (TMDs). The research uses a scanning single-electron transistor (SET) to measure local electronic compressibility and to image charge distribution in moiré TMD systems. The primary goals include: 1) measuring the energy gaps and excitations of correlated electronic ground states; 2) imaging charge ordered phases, such as stripes and generalized Wigner crystals and their melting; and 3) probing the dependence of these emergent states on magnetic field, doping, and twist angle to map out the triangular Hubbard model phase diagram. Moiré TMD systems provide unprecedented flexibility for quantum simulation across a wide swath of Hubbard model parameter space. As a local thermodynamic probe of electronic properties, the SET provides unique insight into this strongly correlated materials platform. In addition, graduate and undergraduate students gain experience in the area of van der Waals assembly and low-temperature scanning probe microscopy.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.