CAREER: Electrically tuned topological phase transitions in moire heterostructures

Stanford University, Stanford CA

Investigators

Abstract

Non-technical abstract Recent advances in isolating and manipulating atomically thin materials provide new approaches to tailor material properties. Such two-dimensional systems are both highly sensitive to their environment and they can be stacked so that properties from one layer influence adjacent layers. This project involves combining dissimilar materials so that one both acts as a sensor for and can modulate the electronic properties of the other. In particular, twisting one layer relative to another induces strong interactions between the electrons in them. Modifying the number of electrons in a third nearby layer enables control over the strength of interactions and can change electronic properties such as the distribution of charge at the nanoscale. Furthermore, the reverse process, where the nanoscale charge arrangement imprints a reconfigurable modulation on the third layer, can also lead to exotic quantum behavior. The predicted states may have applications in low-power electronics, fault-tolerant quantum computing, and novel electromagnetic devices. The project also trains undergraduate and graduate students for careers in quantum technology, builds a library of non-technical videos introducing fields of physics, and inspires the next generation of researchers by developing and implementing hands-on high school instructional modules. Technical abstract Stacking van der Waals materials into heterostructures provides unprecedented flexibility to engineer emergent electronic phases. This project investigates hybrid moiré systems in which a twisted transition metal dichalcogenide (TMD) is separated from a bilayer graphene flake by a thin spacer. In this geometry, the graphene both acts as a sensor and can be used to tune among correlated and topological ground states of the twisted TMD. The research focuses on thermodynamic measurements addressing the order and spin/valley character of the ground states and excitations. Primary goals include: 1) exploring the topological phase diagram of twisted TMDs as a function of displacement field; 2) investigation of ferroelectricity and novel Hubbard model geometries; and 3) using the TMD moiré lattice to imprint a reconfigurable periodic potential on the graphene to study Hofstadter butterfly physics. The research is intertwined with parallel educational goals, including development of instructional modules demonstrating key concepts of topology and geometry, and building a library of non-technical videos introducing research subfields. In addition, undergraduates, graduate students, and high school teachers gain direct laboratory experience in the area of van der Waals assembly and low-temperature electronic measurements. 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.