Optical Plasmon Excitation in Transparent Conducting SrNbO₃ and SrVO₃ Thin Films

Transparent and metallic oxides based on 3d and 4d metals are promising materials for plasmonics. Here, the growth window to obtain epitaxial SrNbO3 (4d(1)) 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 omega(p). Similar features are observed in SrVO3 (3d(1)) films. Optical losses display well pronounced maxima at the corresponding omega(p). Polarization-dependent optical transmittance measurements and ellipsometric data show a dip at omega(p), 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.