Origin of quasilocal plasmons in Nb-substituted EuTiO3

Abstract

Doped perovskite oxides are promising ``material building blocks'' for achieving tunable and intrinsically low-loss plasmonic features in the visible- to near-infrared range, which are unlikely to obtain from conventional plasmonic materials. Here, using a combination of spectroscopic ellipsometry, soft x-ray absorption, x-ray photoemission, and ultraviolet photoemission spectroscopic measurements we observe an unconventional tunable low-loss quasilocal plasmon in the IR energy (1 eV) range in the Nb-substituted perovskite oxide $\mathrm{EuTi}{\mathrm{O}}_{3}$ ($\mathrm{EuT}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{b}}_{x}{\mathrm{O}}_{3}$). This low-loss plasmon oscillation is formed by many-body interactions, an interplay of quasifree ${d}^{1}$ electrons and hybridizations of Eu 4f-Ti $3d$ and O 2p-Ti $3d$. We find that the Nb substitution at Ti site modifies the $\mathrm{Ti}{\mathrm{O}}_{6}$ octahedral tilting and, consequently, alters the electronic structure. Our study reveals the importance of charge, orbital, and lattice to generate plasmons in $\mathrm{EuT}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{b}}_{x}{\mathrm{O}}_{3}$.