Generation of multiple plasmons in strontium niobates mediated by local field effects

Recently, an anomalous generation of multiple plasmons with large spectral weight transfer in the visible to ultraviolet range (energies below the band gap) has been experimentally observed in the insulatinglike phase of oxygen-rich strontium niobium oxides (SrNbO_{3 +δ}). Here, we investigate the ground-state and dielectric properties of SrNbO_{3 +δ} as a function of δ by means of extensive first-principle calculations. We find that in the random phase approximation by taking into account local field effects, our calculations are able to reproduce both the unconventional multiple generations of plasmons and the spectral weight transfers, consistent with experimental data. Interestingly, these unconventional plasmons can be tuned by oxygen stoichiometry as well as microscopic superstructure. This unusual predominance of local field effects in this class of materials is ascribed to the strong electronic inhomogeneity and high polarizability and paves a new path to induce multiple plasmons in the untapped visible to ultraviolet ranges of insulatinglike oxides.