Spin currents in polariton waveguides driven by bright and dark excitons.

Bright and dark excitons in WS2 exciton-polariton waveguides enable an optical spin Hall effect that yields eight polarization domains and spin-polarized currents propagating up to 92 ± 1 μm at room temperature.

• Why it matters: Photonic spin-orbit coupling can separate circular polarization domains, but it is ineffective for incoherent photoluminescence, motivating a polaritonic route that can harness incoherently populated excitons.
• What they did: WS2 monolayers were embedded in waveguide microcavities to form exciton-polaritons; under non-resonant pumping, strongly populated dark excitons fed both transverse-electric-like and transverse-magnetic-like polariton modes with out-of-plane electric-field components.
• The result: The resulting waveguide polaritons exhibit the optical spin Hall effect, producing eight polarization domains and spin-polarized polariton currents that propagate up to 92 ± 1 μm at room temperature, supporting room-temperature spin-optoelectronic device potential.

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