Reducing surface depletion of superconducting SrTiO3 films with EuTiO3 capping layers

Doped SrTiO3 thin films are of significant scientific interest for their superconducting, ferroelectric, and thermoelectric properties. Air-exposed thin films of doped SrTiO3 suffer from surface carrier depletion that makes it difficult to obtain thin, conducting films, especially at low doping densities and temperatures. Here, we show that thin (10 nm) EuTiO3 capping layers can prevent surface depletion and allow for conducting heterostructures with SrTiO3 films as thin as 10 nm. We also investigate the superconducting properties of EuTiO3 capped SrTiO3 films. We show that the superconducting transition temperature decreases systematically as the SrTiO3 film thickness is reduced, which is likely due to proximity effects.