Suppression of p-Wave Altermagnetism by Localized 4f Electrons in CeNiAsO

Altermagnetism, characterized by momentum-dependent spin splitting and zero net magnetization, has so far been explored mainly in weakly or moderately correlated d-electron systems. How such symmetry-allowed band splitting manifests in heavy-fermion materials, where magnetic exchange competes with Kondo correlations, remains unclear. Here we use high-resolution angle-resolved photoemission spectroscopy to investigate CeNiAsO, a heavy-fermion candidate for p-wave altermagnetism. Despite macroscopic signatures consistent with the proposed p-wave magnetic order, we find no resolvable near-Fermi-level p-wave exchange splitting on the Ni 3d-derived conduction bands across the Neel transitions. Fermi-surface mapping, orbital-resolved ARPES identify that the low-energy electronic structure is dominated by Ni 3d bands, while resonant photoemission reveals that the Ce 4f states remain predominantly localized with residual c-f hybridization. First-principles calculations further show that an uncorrected itinerant-4f description produces dispersive Ce 4f bands and additional Fermi-surface pockets that are absent in experiment, thereby overestimating both the low-energy c-f hybridization and the exchange splitting transferred to the Ni 3d bands. When the localized Ce 4f character is incorporated through DFT+U , the experimental Fermi-surface topology is recovered and the residual p-wave splitting on the Ni 3d-derived bands is reduced to only a few meV, below the effective experimental resolution. These results identify CeNiAsO as a strongly correlated f-electron limit of p-wave magnetism, in which localized 4f electrons suppress the observable single-particle band-splitting signature expected from a weak-correlation picture.