Altermagnetism features momentum-dependent spin splitting without net magnetization, extending spintronics beyond conventional ferromagnetism and antiferromagnetism. However, the photonic realization of altermagnetism has remained a formidable challenge due to the fundamental differences between fermionic electrons and bosonic photons. Here, we report the first experimental realization of an orbital altermagnetic photonic crystal, based on an antiunitary C4zT symmetry enforced correspondence between a local p-orbital σ/π doublet and crystal momentum. We experimentally demonstrate that the resulting system exhibits momentum-dependent spin splitting with alternating pseudospin polarization and a dxy-wave form factor, as confirmed by measured band structures and iso-frequency contours. Moreover, we show that the orbital altermagnetic photonic crystal supports unique pseudospin-selective transport of electromagnetic waves, including photonic pseudospin splitting and pseudospin filtering. Our results extend the field of alternagnetism to photonic systems, opening a new avenue for designing spinphotonic devices.
@article{arxiv.2605.28656,
title = {Orbital Altermagnetic Photonic Crystal},
author = {Sichang Qiu and Huichang Li and Yan Meng and Xiang Xi and Zebin Zhu and Ce Shang and Zhen Gao and Tie Jun Cui and Shuo Liu},
journal= {arXiv preprint arXiv:2605.28656},
year = {2026}
}