Hyperbolic Exciton Polaritons in a van der Waals Magnet: Article No. 8261

Francesco Ruta, Shuai Zhang, Yinming Shao, Samuel Moore, Swagata Acharya, Zhiyuan Sun, Siyuan Qiu, Johannes Geurs, Brian S. Y. Kim, Matthew Fu, Daniel G. Chica, Dimitar Pashov, Xiaodong Xu, Di Xiao, Milan Delor, X.-Y. Zhu, Andrew Millis, Xavier Roy, James Hone, Cory DeanMikhail Katsnelson, Mark van Schilfgaarde, D. Basov

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1 Scopus Citations


Exciton polaritons are quasiparticles of photons coupled strongly to bound electron-hole pairs, manifesting as an anti-crossing light dispersion near an exciton resonance. Highly anisotropic semiconductors with opposite-signed permittivities along different crystal axes are predicted to host exotic modes inside the anti-crossing called hyperbolic exciton polaritons (HEPs), which confine light subdiffractionally with enhanced density of states. Here, we show observational evidence of steady-state HEPs in the van der Waals magnet chromium sulfide bromide (CrSBr) using a cryogenic near-infrared near-field microscope. At low temperatures, in the magnetically-ordered state, anisotropic exciton resonances sharpen, driving the permittivity negative along one crystal axis and enabling HEP propagation. We characterize HEP momentum and losses in CrSBr, also demonstrating coupling to excitonic sidebands and enhancement by magnetic order: which boosts exciton spectral weight via wavefunction delocalization. Our findings open new pathways to nanoscale manipulation of excitons and light, including routes to magnetic, nonlocal, and quantum polaritonics.
Original languageAmerican English
Number of pages9
JournalNature Communications
StatePublished - 2023

NREL Publication Number

  • NREL/JA-5K00-88152


  • hyperbolic exciton
  • magnetic properties and materials
  • polaritons
  • sub-wavelength optics
  • two-dimensional materials
  • Van der Waals magnet


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