Nonlinear coupling of interlayer excitons in van der Waals heterostructures to plasmonic and dielectric nanocavities

Principal investigators:

• Mirko Cinchetti
• Klaus Jöns, Thomas Zentgraf (University Paderborn)

Summary:

Quantum light sources based on 2D materials have been the topic of extensive research in the past years. However, the generation of indistinguishable photons from such emitters has proven to be elusive, due to the strong spectral jittering of the quantum emitter. One possible solution is coupling interlayer excitons to nanocavities taking advantage of Purcell enhancement. Interlayer excitons can be found in van der Waals heterostructures, that consist of layers of different 2D materials stacked together. In such heterostructures, the combination of semiconductors with different bandgaps and a controlled mutual rotation leads to the formation of so-called Moiré patterns for excitons, which allows designing a large variety of quantum optical materials. Importantly, the Moiré pattern is expected to form a periodic confining potential for the interlayer excitons, creating an array of quantum emitters. Thanks to their large permanent dipole the transitions of these emitters can be tuned over a large energy range, making them ideal candidates for coupling to nanocavities. Despite major efforts taken to investigate 2D quantum emitters, little insights have been gained to understand the fundamental properties of Moiré trapped excitons.

The main focus of this project is on the properties of interlayer excitons trapped in the controllable superlattices that naturally arise in Moiré patterns. We will focus on the behavior of interlayer excitons as single-photon emitters, which is directly related to their quantum confinement and the orientation of the excitons’ electric dipole. In particular, we will explore strategies to increase the quantum yield of single-photon emitters by optimizing their electric dipole and by coupling them to plasmonic/dielectric nanocavities.

The realization of van der Waals heterostructures with high quality and precision and their well-determined coupling to nanocavities requires a tremendous technological effort, both in terms of high-quality sample preparation as well as of characterization of the heterostructures’ properties. To tackle these challenges at best, the project is organized in 5 strongly interrelated work packages. In particular, we will study the nonlinear coupling of different kinds of nanoresonators made of noble metals like gold and silver (supporting localized surface plasmon resonances) as well as high-index materials like silicon and gallium arsenide (supporting Mie-type resonances) with the heterostructures before and after deposition on the nanocavities. At the same time, we will use photoemission electron microscopy to determine the spatial localization of the near field of the plasmonic nanoresonators and angle-resolved photoelectron spectroscopy to gain information about the wavefunction of interlayer excitons. Information about the orientation of the electric dipole of the interlayer excitons will be used to optimize the quantum optical properties of the structures, which will be investigated using cryogenic micro-photoluminescence spectroscopy and correlation measurements. The nanoresonators will also provide an additional degree of freedom for the tailoring of the emission into the far-field. This will enable the first realization of an efficient cavity coupled quantum light source based on Moiré interlayer excitons with the potential of generating indistinguishable photons for the first time from 2D quantum emitters.