New metallic interface state in oxide artificial superlattices investigated by optical spectroscopy

Interfaces between the artificial structures of oxides have been attracting a lot of attention because of their novel physical properties, which are usually not obtained in single-phase bulk materials. As a model system to understand the interfaces between the Mott insulators and the band insulators, high quality artificial superlattices of SrTiO$_{3}$ / LaTiO$_{3}$ were epitaxially grown by pulsed laser deposition equipped with reflection high energy electron diffraction. Mid infrared-visible optical transmittance and reflectance spectra were measured to show highly conducting interface, providing clear evidences for electronic reconstruction at the interface. Moreover, temperature-dependent infrared ellipsometry results showed that the interface state was different from conventional metal, indicating a new two dimensional metallic state.