From catalysis and flat panel displays to photovoltaics, transparent and conducting transition metal oxides are gaining momentum toward more sustainable and cost-efficient applications.
Here it is shown that, without using phase-matching arrangements, bulk plasmons can be excited in continuous epitaxial films of metallic SrVO3 and SrNbO3, with plasma absorption edges at visible range, and tuned mainly by electron correlations and phonon dressing. Films can be made reflective or transparent at whish.
Transparent and metallic oxides based on 3d and 4d metals are promising materials for plasmonics. Here, the growth window to obtain epitaxial SrNbO3 (4d1) thin films is determined and the role of substrates to achieve optimal electrical conductivity and the largest residual resistivity ratio is disclosed. Optical measurements on optimized films indicate a large transparency at the visible with a sharp edge at about 1.9 eV, which coincides with the zero-crossing of the permittivity, allowing to identify the plasma frequency ωp. Similar features are observed in SrVO3 (3d1) films. Optical losses display well pronounced maxima at the corresponding ωp. Polarization-dependent optical transmittance measurements and ellipsometric data show a dip at ωp, occurring for p- but not s-polarized light, which is a fingerprint of optical bulk plasmon excitation. Remarkably, plasmon resonance is achieved here by using oblique incidence of light rather than phase-matching arrangements, and by exploiting charge density gradients at the film surface. This observation points to new opportunities for engineering plasmons in heterostructures.