Unconventional multiple plasmons generation in Oxygen-rich Strontium Niobate mediated by Local Field Effects*

Recently, an anomalous form of plasmons have been observed experimentally in Oxygen-rich Strontium Niobate Oxides (SrNbO_3+δ). These new plasmons have multiple frequencies in the visible to ultraviolet ranges and were believed to be connected with the strongly correlated electrons induced by spatial confinement. Here we theoretically investigate the origin of plasmons generation by means of first principle calculations. In the framwork of the Random Phase Approximation (RPA), we infer that the spectral weight transfer and the multiple formation of plasmon frequencies can be ascribed to the dielectric function local fluctuations called Local Field Effects (LFEs). We proved that the LFEs are unusually predominant with formation of plasmons in materials with strong electrical inhomogeneity and high polarizability.