Moiré superlattices emerge when two stacked materials have a slight lattice or angle mismatch, forming interference patterns with enlarged real-space periodicity and reduced bandwidth in the momentum space. They have offered a new paradigm for the study of strong electronic correlations, non-trivial band topology, and various emergent phenomena. Prof. Xu started to work on twisted bilayer graphene back to 2016. At N08, we build different types of moiré superlattices and investigate them from multiple perspectives such as the electronic transport and optical spectroscopy.The flatbands and quenched kinetic energy allow us to observe the abundance of correlated insulating states at fractional fillings in moiré heterobilayer WSe2/WS2 (ref.5). We have been able create moiré magnet (twisted bilayer CrI3) and observe the coexistance of ferromagnetic and antiferromagnetic ground states (ref.4), indicating that the stacking and angle-misalighment of 2D magnets can have profound effect on their magnetic properties. Recently, we have observed the trapping and manipulation of Rydberg excitons by moiré potentials (ref.1).

We are working on fabricating high-quality nano-devices based on topological materials and exploring interface engineering. This development aims to facilitate the study of their intrinsic transport properties, the role of electron-electron interactions, topological phase transitions, and potential applications in topological electronics and spintronics. Additionally, we will explore the growth methods for new types of magnetic thin films with topological electronic band structures, aiming to reveal novel transport properties arising from the interplay between topology, magnetism, and strong correlations.

Materials without inversion center is an intriguing platform hosting multiple orders and non-trivial topological properties. The synergetic interplay between these degrees of freedom leads to rich quantum phenomena which can be captured by magneto-transport measurements at low temperatures. One example is the counterintuitive yet experimentally verified finite-momentum pairing state [1]. The ongoing project focuses on its possible existence and other unconventional pairing schemes in a variety of van der Waals heterostructures. Symmetry, ferroelectricity [2] and the Berry phase are considered as key parameters in understanding novel experimental implications in these systems. The project is supported by the National Science Foundation of China and the Ministry of Science and Technology.

Rydberg excitons are highly excited electron-hole pairs generated through photon excitation in semiconductors. In recent years, with the development in the field of two-dimensional materials, the study of Rydberg excitons has gradually extended into two-dimensional space. The solid-state nature of Rydberg excitons, combined with their large dipole moments, strong mutual interactions, and greatly enhanced interactions with the surroundings, holds promise for a wide range of applications in sensing, quantum optics, and quantum simulation. For instance, their sensitivity to dielectric screening can be utilized to explore novel quantum states and quantum phase transitions in proximity to two-dimensional electronic systems, known as Rydberg sensing—a technique that we have pioneered (ref. 2 and 3). By employing the moiré potential generated in two-dimensional moiré superlattices, spatial confinement and manipulation of these Rydberg excitons can be achieved, leading to the discovery of Rydberg moiré excitons in the strong coupling limit (ref. 1).

We are presently in the process of developing an experimental setup that will enable in-situ pressure adjustments for nano-devices constructed from low-dimensional quantum materials. The application of hydrostatic pressure proves to be an effective pathway for reducing the van der Waals gap between layers and significantly enhancing interlayer hybridizations.