Abstract
Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible–ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1−xNb1−yO3+δ family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible–ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials.
Highlights
Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities
Transport measurements reveal that lp-SNO and mp-SNO are metallic with room-temperature resistivity of 1 Â 10 À 4 and 6 Â 10 À 3 O cm, respectively, while hp-SNO is insulator-like with room-temperature resistivity of 6 O cm
The presence of extra oxygen planes in hp-SNO and their absence in lp-SNO accompanied by remarkable changes in e(o) and s1(o) spectra indicate that the interplay between extra oxygen planes and electronic correlations plays important roles in the plasmonics excitations and metal–insulator transition (MIT) between the films
Summary
Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. We discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1 À xNb1 À yO3 þ d family These correlated plasmons have multiple plasmon frequencies and low loss in the visible–ultraviolet range. Several Sr1 À xNbO3 þ d films with varying oxygen content, electrical conductivity (from metallic to insulator-like) and film thicknesses are studied using spectroscopic ellipsometry (SE), atomic-resolution transmission electron microscopy (TEM), transport measurements and supported by theoretical calculations based on coupled harmonic oscillators model and density functional theory. These correlated plasmons arise from collective excitations of correlated electrons in the film, where the nanometre-spaced confinement of extra oxygen planes causes increased Coulomb repulsions among the electrons. The decrease of extra oxygen plane density increases the electrical conductivity, and, as correlated plasmons are vanishing in the metallic films, the increased free-charge density causes conventional plasmon to arise at B1.9 eV
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