Abstract

The optical properties of low-dimensional semiconductor nanostructures are often governed by excitons – quasi-particles formed by a photo-generated electron and hole bound together by Coulomb attraction. Strong excitonic effect, particularly pronounced in two-dimensional (2D) van der Waals semiconductors, provides an unprecedented platform for studying exciton quasiparticles, which exhibit different charges, spins, or spatial configurations.

Here I will explore the excitonic landscape in 2D semiconductors and van der Waals heterostructures. One prominent example is the 2D Ruddlesden–Popper metal-halide perovskites (2DP), where the soft, polar, and low-symmetry lattice creates a unique environment for electron-hole interactions, offering a fascinating playground for studying exciton physics. Some aspects of this system, however, remain challenging to fully understand. I will highlight the controversy surrounding the unexpectedly high light emission efficiency of this material and show that it can be explained by the interplay between phonons and the exciton fine structure.

I will further discuss the excitonic properties in homo-bilayer transition metal dichalcogenides where the interaction between two dipolar excitons with opposite dipole moments can lead to the formation of a new type of interlayer exciton, namely a quadrupolar exciton. And finally, I will demonstrate that excitonic effect are very pronounced in recently discovered 2D magnetic semiconductors. This brings new possibilities for investigating fundamental interactions between excitons and a correlated spin environment, particularly pronounced in CrSBr. I will demonstrate that CrSBr hosts both localized Frenkel-like and delocalised Wannier-Mott-like excitonsa duality rare among other magnetic or nonmagnetic 2D materials.