Theoretical Study of Unconventional Plasmons Formation within a Reduced-Size 1D Hubbard Model around a Quarter Filling

Abstract

Plasmons, which are conventionally known as quanta of electron plasma oscillations in a metal, were discovered unconventionally in an experiment of Strontium Niobate Oxide with oxygen enrichment (SrNbO3,4). Plasmons that revealed in this experiment arose in the visible-ultraviolet range due to a confinement created by additional oxygens forming nanometer-spaced planes. This experimental background motivated us to study the formation of unconventional plasmons in the material by modeling a hypothetical system described by 5-sites linear chain Hubbard model around a quarter filling. The model was then solved by exact diagonalization (ED) method, from which we constructed the corresponding retarded Green function via Lehmann representation. Our interest was to calculate the optical response functions using Kubo formula of the linear response theory. Our results showed that the conventional plasmonic signals got modified by the presence of on-site Coulomb interactions. In addition, we observed that unconventional plasmons, behaving similarly to those found in the experiment, arose when the Coulomb intersite interaction was applied to the calculation.