Spin-excitation response to oxygen deficiency in La₃Ni₂O_7-δ thin films

Oxygen stoichiometry has been identified as a key parameter controlling superconductivity in the bilayer nickelate La₃Ni₂O_7-δ. Using resonant inelastic x-ray scattering, we systematically investigate the evolution of orbital and spin excitations in La₃Ni₂O_7-δ thin films with varying oxygen content. In vacuum-annealed samples, the suppression of the 1.6 eV dd excitation under π polarization reflects appreciable inner apical-oxygen vacancies, which locally disrupt the out-of-plane p-d hybridization and the corresponding interlayer superexchange pathways. Nevertheless, the oxygen-deficient films exhibit spin excitations originating from Q = (0.25, 0.25) with a similar dispersion to the as-grown sample, suggesting a mixed ground state of double spin stripe and spin-charge stripe orders with nearly identical spin correlations. By contrast, the magnon damping rate is slightly enhanced in the vacuum-annealed sample, reflecting a modest increase in electronic disorder associated with oxygen defects. Collectively, these findings reveal that short-range spin correlations in La₃Ni₂O_7-δ are insensitive to oxygen-vacancy-induced perturbations, including electron doping and local disruption of interlayer superexchange pathways, even in samples with appreciable oxygen deficiency, where the 1.6 eV dd excitation associated with Ni 3d_z²-O 2p_z hybridization is suppressed by up to 58%.