Emergent quantum properties from low-dimensional building blocks and their superlattices

Low-dimensional materials, with the highly tunable electronic structures depending on their sizes and shapes, can be exploited as fundamental building blocks to construct higher-order structures with tailored emergent properties. This is akin to molecules or crystals that are assembled by atoms with diverse symmetries and interactions. Prominent low-dimensional materials developed in recent decades include 0D quantum dots, 1D carbon nanotubes, and 2D van der Waals materials. These materials enclose a vast diversity of electronic structures ranging from metals and semimetals to semiconductors and insulators. Moreover, low-dimensional materials can be assembled into higher-order architectures known as superlattices, wherein collective electronic and optical behaviors emerge that are absent in the individual building blocks alone. Superlattices composed of interacting low-dimensional entities thus define an ultra-manipulatable materials platform for realizing artificial structures with customizable functionalities. Here, we review significant milestones and recent progresses in the field of low-dimensional materials and their superlattices. We survey recently observed exotic emergent electronic and optical properties in these materials and delve into the underlying mechanisms driving these phenomena. Additionally, we hint the future opportunities and remaining challenges in advancing this exciting area of research.