# Circularly Polarized Polariton Lasing from Spin‐Momentum Locking in Deformed Plasmonic Kagome Cavities

## TL;DR

This paper presents a method to achieve polariton lasing with high circular polarization using deformed plasmonic Kagome cavities at room temperature.

## Contribution

The study introduces spin-momentum locking in deformed Kagome lattices to enable controlled circular polarization in polariton lasing.

## Key findings

- Deformed Kagome lattices produce circularly polarized lattice resonances with high polarization degrees.
- Six lasing beams from T points show alternating handedness and low lasing thresholds.
- The technique opens new avenues for optical analogues of spin and valley physics.

## Abstract

This paper describes room‐temperature polariton lasing with high circular polarization from plasmonic Kagome lattice cavities strongly coupled to colloidal semiconducting quantum wells. By shrinking and expanding the trimer unit cells in Al nanoparticle lattices, the inversion symmetry is broken, resulting in the spin‐momentum locking of cavity photons. Circularly polarized lattice resonances emerged from crossings of different diffraction orders, denoted as T points, along the Γ‐K direction in momentum space and whose degree of circular polarization is higher than those of high‐symmetry K‐points. Deformed Kagome lattice cavities combined with CdSe nanoplatelets enabled the formation of exciton‐polaritons. Spin‐selectivity from cavity modes resulted in control over the handedness of circular polarization as well as direction of photoluminescence from lower polaritons. Six lasing beams from T points has alternating handedness, low thresholds (8 µJ cm−
2), and high degrees of circular polarization (≈0.7). The anticipation that spin‐momentum locking via plasmonic Kagome lattices can be extended to other non‐Bravais metasurfaces with hexagonal symmetries and opens prospects for exploring optical analogues of spin and valley physics.

This paper describes room‐temperature polariton lasing with high circular polarization from deformed plasmonic Kagome lattice cavities strongly coupled to colloidal CdSe nanoplatelets. Spin‐selectivity from cavity modes resulted in control over the handedness of circular polarization as well as the direction of polariton lasing, opening prospects for exploring optical analogues of spin and valley physics.