Physics Department -  Emergent Tunability of Excitonic Interactions and Superlattices in Complex Two-Dimensional Heterostructures

Abstract
Interfaces between two-dimensional (2D) materials offer a fertile ground for emergent structures and functionalities, most notably, moiré superlattices formed in twisted bilayers that can host correlated and superconducting states. Recent studies in graphene systems have demonstrated that even richer superlattice structures and electronic behaviors can emerge in beyond-bilayer heterostructures. However, achieving such exquisite structural and interactional control in semiconducting 2D materials has remained elusive. In this talk, I will discuss two of our recent efforts to address this challenge. First, I will introduce a new excitonic material platform based on a tetralayer 2D semiconductor heterostructure that hosts a highly polarizable interlayer exciton species. In this system, the exciton dipole length, in-plane radius, and binding energy can be continuously tuned in situ over a broad range, allowing direct control over exciton–exciton interactions and the nature of excitonic many-body phase transitions. These results establish exciton geometry as a new, continuously tunable materials parameter and open pathways toward exciton-based quantum phase-transition simulators. Second, I will present our design of emergent supermoiré lattices in a hetero-tetralayer system, where two distinct yet highly interfering bilayer moiré superlattices coexist. By tuning the relative stacking order (R- vs. H-type) and twist angle between the parental bilayers, we achieve new classes of long-range supermoiré patterns that are fundamentally inaccessible in conventional bilayer systems. Together, these studies demonstrate how crafting complex 2D heterostructures enables nontrivial control over both electronic interactions and structural landscapes, offering new opportunities in quantum materials design and discovery.