Luminescence anomaly of dipolar valley excitons in homobilayer semiconductor moir\'e superlattices

TL;DR

This paper uncovers a luminescence anomaly in moiré superlattices of twisted homobilayer transition metal dichalcogenides, revealing how tiny displacements dramatically alter exciton brightness and polarization, with implications for quantum photonics.

Contribution

It demonstrates the luminescence anomaly caused by spatially varying layer configurations and exciton interactions in moiré superlattices, a novel insight into exciton behavior in these materials.

Findings

Tiny displacements significantly increase brightness and change polarization.

Luminescence predominantly occurs at edges and vacancies at full filling.

Chains of polarization entangled photons are produced in cascaded emissions.

Abstract

In twisted homobilayer transition metal dichalcogenides, intra- and inter-layer valley excitons hybridize with the layer configurations spatially varying in the moir\'e. The ground state valley excitons are trapped at two high-symmetry points with opposite electric dipoles in a moir\'e supercell, forming a honeycomb superlattice of nearest-neighbor dipolar attraction. We find that the spatial texture of layer configuration results in a luminescence anomaly of the moir\'e trapped excitons, where a tiny displacement by interactions dramatically increases the brightness and changes polarization from circular to linear. At full filling, radiative recombination predominantly occurs at edges and vacancies of the exciton superlattice. The anomaly also manifests in the cascaded emission of small clusters, producing chains of polarization entangled photons. An interlayer bias can switch the superlattice into a single-orbital triangular lattice with repulsive interactions only, where the luminescence anomaly can be exploited to distinguish ordered states and domain boundaries at fractional filling.