A New 'Bichromatic' Crystal Sandwich Tunable for Quantum Light

In the quest to engineer new quantum materials, researchers have successfully realised a 'bichromatic' moiré superlattice using a specific trilayer of transition metal dichalcogenides. By stacking layers of tungsten diselenide (WSe₂) and tungsten disulfide (WS₂) in an asymmetric sandwich, the team created a structure where the atomic patterns overlap to form a complex, larger-scale interference pattern known as a moiré superlattice.

This novel configuration is unique because it combines different stacking orientations with mismatched wavelengths, resulting in a highly tunable environment. Within this landscape, the researchers observed the emergence of 'fermionic quadrupolar moiré trions'. These are complex quasiparticles formed by an interlayer exciton—an electron and a hole in different layers—bound to an additional hole in the opposite layer. Crucially, these trions possess vanishing dipole moments, making them distinct from standard excitons.

The study demonstrates that applying an out-of-plane electric field can effectively reshape these moiré excitons. This control allows scientists to drive a transition between different electronic states, specifically shifting from interlayer to intralayer Mott states characterised by enhanced Coulomb repulsion. This ability to tune interactions and optical properties positions these bichromatic superlattices as a promising, reconfigurable platform for generating entangled quantum light and advancing spin-photon engineering.