Optical spectroscopy of reconstructed and moiré van-der-Waals bilayers

The field of conventional silicon-based electronics is approaching its quantum-mechanical limits, making further miniaturization increasingly challenging. To overcome these constraints, alternative low-dimensional semiconductors and novel device architectures are being explored, enabling new ways to manipulate information carriers such as photons, excitons, and spins. In this work, van der Waals bilayers, consisting of transition-metal dichalcogenide monolayers, are investigated using optical spectroscopy. These materials exhibit a direct band gap, strongly bound excitons, and valley-selective spin properties, making them promising platforms for quantum optoelectronics. By controlling the layer composition and stacking angle, the electronic band structure can be engineered, giving rise to rich physical phenomena, such as hybridization. A key parameter is the lattice constant of the resulting superlattice, which determines lattice vibrations and excitonic behavior and may induce atomic reconstruction. Here, we explore how lattice vibrations and excitonic properties can be tailored both in regular moiré lattices and in systems exhibiting atomic reconstruction, revealing new possibilities for controlling quantum states in two-dimensional materials.