In a joint theory–experiment study published in npj 2D Materials and Applications, Habib Rostami from the University of Bath, together with Emmanuele Cappelluti (CNR-ISM, Trieste) and Federico Cilento (Elettra-Sincrotrone Trieste), have shown that apparently inversion-symmetric bulk WSe₂ hides a robust internal orbital order that can be switched and read out with ultrafast light pulses. By driving the crystal with circularly polarised laser pulses and measuring ultrafast Kerr rotation, the team reveals clear A-, B- and C-exciton signatures linked to orbital and spin Berry curvature. Their results demonstrate that this orbital order is “hidden” in the form of a hybrid valley–layer polarisation in a centrosymmetric layered material, yet it can generate strong macroscopic optical effects, opening new routes to bulk-based optoelectronic, valleytronic and orbitronic devices. F.C. conceived and conducted the experiments, while E.C. and H.R. developed the theory.

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Emmanuele Cappelluti, Habib Rostami & Federico Cilento
"Hidden order revealed by light-driven Kerr rotation in centrosymmetric bulk WSe2"
npj 2D Materials and Applications volume 9, Article number: 89 (2025)