Room-Temperature Spin Currents Ride Waveguide Polaritons Fed by Dark Excitons

Physicists have coaxed spin-polarized light currents through microscopic waveguides at room temperature, a feat that could bring spin-based optoelectronics out of the cryostat and onto ordinary lab benches. In a study published in Nature Materials, researchers including Qiuyu Shang and Weibo Gao embedded WS2 monolayers in waveguide microcavities and demonstrated strong coupling between bright excitons and photonic modes, forming exciton–polaritons — hybrid particles of light and matter — that carry spin-polarized currents over distances exceeding 90 micrometers at room temperature.

The work, described in the journal's abstract as demonstrating waveguide exciton–polaritons that transport spin-polarized currents up to 92 ± 1 micrometers, tackles a long-standing frustration in the field. The optical spin Hall effect, which enables the spatial separation of four domains of circularly polarized light from a linearly polarized source through photonic spin–orbit coupling, is ineffective for incoherent photoluminescence. For ordinary incoherent photoluminescence, the mechanism simply does not work, limiting practical routes to spin-controlled light flows.

The key insight lies in the peculiar anatomy of excitons in transition metal dichalcogenide monolayers. Bright excitons in these materials possess in-plane electric dipoles and strong oscillator strengths, making them natural partners for photons. Dark excitons, by contrast, carry out-of-plane dipoles and are typically invisible to far-field detection. By embedding WS2 monolayers in waveguide microcavities, the researchers demonstrated strong coupling between bright excitons and photonic modes, forming exciton–polaritons that inherit both light’s mobility and excitons’ spin structure.

Under non-resonant pumping — essentially illuminating the sample without fine-tuning the laser to a specific transition — dark excitons became strongly populated and fed both transverse-magnetic-like and transverse-electric-like exciton–polariton modes, each carrying an out-of-plane electric-field component. Under non-resonant pumping, dark excitons become strongly populated and feed both transverse-magnetic- and transverse-electric-like exciton–polariton modes, each with an out-of-plane electric-field component, and the researchers observe the optical spin Hall effect in these waveguide polaritons.

The result is a striking pattern: the optical spin Hall effect in waveguide polaritons produces eight distinct polarization domains, within which spin-polarized polariton currents propagate up to 92 ± 1 micrometers at room temperature. The researchers observe spin-polarized polariton currents propagating up to 92 ± 1 micrometers at room temperature.

Non-resonant excitation means researchers do not need to lock a laser to a precise energy or momentum state to populate the polariton modes.

The theoretical framework, developed in collaboration with Guillaume Malpuech and Dmitry Solnyshkov, connects the observed polarization domains to the non-degenerate transverse-electric and transverse-magnetic modes of the waveguide.

Figures in the published article trace the progression from basic materials characterization to the full spin Hall measurement, including illustrations of TMD-based excitons and in-plane microcavities, room-temperature waveguide polaritons, enhanced light–matter interaction in the polaritonic waveguides, and the optical spin Hall effect in a square microcavity.

The researchers argue that these results establish transition metal dichalcogenide-based polaritonic waveguides as a promising platform for room-temperature spin-optoelectronic devices. These results establish transition metal dichalcogenide-based polaritonic waveguides as a promising platform for room-temperature spin-optoelectronic devices.

Subject of Research: Room-temperature spin-polarized exciton–polariton currents in WS2 waveguide microcavities driven by bright and dark excitons

Article Title: Spin currents in polariton waveguides driven by bright and dark excitons

Article References: Shang, Q., Zhang, M., Maggi, M. V., Seet, N. W. E., Dini, K., Zhao, T., Feng, Z., Yang, D., Gromovyi, M., Chenot, S., Alloing, B., Rasmita, A., Malpuech, G., Liew, T. C. H., Solnyshkov, D., Gao, W., & Zúñiga-Pérez, J. (2026). Spin currents in polariton waveguides driven by bright and dark excitons. Nature Materials. https://doi.org/10.1038/s41563-026-02782-5

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02782-5

Keywords: exciton–polaritons, WS2, spin currents, optical spin Hall effect, waveguide microcavities, dark excitons, transition metal dichalcogenides, room temperature, spin–orbit coupling, spin-optoelectronics, Spin, currents