2026/07/16 by Yiwen Song, Peiyi He, Weizhe Zhang +7
#cond-mat.mtrl-sci
We report momentum-resolved measurements of exciton dispersion in multilayer CrSBr using defocus-engineered electron energy-loss spectroscopy, supported by first-principles calculations. A pronounced in-plane anisotropy is observed, with the exciton exhibiting a linear dispersion along ΓY within | \boldsymbolq | < 0.007 Å-1, while remaining nearly dispersionless along ΓX. The slope reaches 7.02 eV Å, among the largest reported in low-dimensional systems. The calculations reproduce the experimentally observed linear dispersion, confirming its intrinsic origin. We attribute the anisotropic dispersion to the long-range electron--hole exchange interaction, enhanced by strong out-of-plane confinement and governed by the directional selection rules of the transition dipole moment. Comparative measurements across the magnetic phase transition from the paramagnetic to the A-type antiferromagnetic state show that the dispersion remains essentially unchanged, indicating negligible coupling between exciton propagation and magnetic order. These results establish CrSBr as a model system for investigating anisotropic exciton dynamics in low-symmetry layered semiconductors.