Engineering Quantum States in Layered Semiconductors

The physical properties of atomic monolayers are often very different from those of their parent bulk materials. Prime examples are graphene and monolayers of MoS2, as their ultimate thinness makes them extremely promising for applications in electronics and optics. At the same time, they give access to new degrees of freedom of the electronic system (such as the valley index) or interactions between quasiparticles such as excitons (Coulomb- bound electron–hole pairs). Here we discuss how our understanding and engineering of exciton states in multi-layers allows tuning the linear and non-linear optical properties in atomically thin materials in the context of collective quantum states. In particular, we study the interactions between intra-layer and inter-layer excitons with different dipoles, as they are tuned into resonance [1]. In homobilayers we show gate-tunable second harmonic generation mediated by interlayer excitons [2]. In heterobilayers we measure the twist angle between the layer in-situ by addressing intralayer exciton resonances in each layer. For heterostructures with close to zero twist angle, we observe changes of exciton resonance energies and the appearance of new resonances in the linear and non-linear susceptibilities [3].<br/>[1] Sponfeldner et al, arXiv:2108.04248<br/>[2] Shree et al, arXiv:2104.01225<br/>[3] Paradisanos et al, arXiv:2110.08095