Excitons in two-dimensional materials and heterostructures: Optical and magneto-optical properties

Two-dimensional (2D) materials are attractive systems to explore exciton physics and possible applications in optoelectronics, opto-spintronics, and quantum technologies. Monolayer transition-metal dichalcogenides (TMDs) are direct gap 2D semiconductor materials with robust excitons and two inequivalent K + and K − valleys. They can be vertically stacked to form van der Waals (vdW) heterostructures with typically Type II band alignment that enables the formation of interlayer excitons (IEs) and creates Moiré patterns. Magnetic 2D materials are also promising systems to explore exciton physics and their correlations with magnetic properties. They can be stacked with TMD materials to form magnetic vdW heterostructures. Their optical properties are strongly dependent on the number of layers, charge transfer, defects, strain, and twist angle stacking, which offer a versatile platform to control their physical properties. Here, we review some recent discoveries on the exciton and valley properties of van der Waals materials and heterostructures. Graphical abstract