Enhanced superconductivity in SrTiO3 -based interfaces via amorphous Al2 O3 capping

Oxide interfaces feature unique two-dimensional (2D) electronic systems with diverse electronic properties such as tunable spin-orbit interaction and superconductivity. Conductivity emerges in these interfaces when the thickness of an epitaxial polar layer surpasses a critical value, leading to charge transfer to the interface. Here, we show that depositing amorphous Al2O3 on top of the polar oxide can reduce the critical thickness and enhance the superconducting properties for SrTiO3-based interfaces. A detailed transmission electron microscopy analysis reveals that the enhancement of the superconducting properties is linked to the expansion of the SrTiO3 lattice in a direction perpendicular to the interface. We propose that the increase in the superconducting critical temperature, Tc, is a result of epitaxial strain.