Concomitant appearance of conductivity and superconductivity in (111)LaAlO3/SrTiO3 interface with metal capping

TL;DR

This study investigates how metal capping layers influence the critical thickness for conductivity and superconductivity at the (111) LaAlO3/SrTiO3 interface, revealing unique behaviors compared to the (100) orientation through experiments and density functional theory.

Contribution

It demonstrates that metal capping layers can significantly reduce the critical thickness for conductivity and superconductivity at the (111) LaAlO3/SrTiO3 interface, with distinct effects compared to the (100) orientation.

Findings

Cobalt capping reduces critical thickness to 3ML.

Platinum capping reduces critical thickness to 6ML.

Conductivity and superconductivity appear concomitantly in (111) interfaces.

Abstract

In polar-oxide interfaces, a certain number of monolayers (ML) is needed for conductivity to appear. This threshold for conductivity is explained by accumulating sufficient electric potential to initiate charge transfer to the interface. Here we study experimentally and theoretically the (111) SrTiO3/LaAlO3 interface where a critical thickness, tc, of nine epitaxial LaAlO3 ML is required to turn the interface from insulating to conducting and even superconducting. We show that tc decreases to 3ML when depositing a cobalt over-layer (capping) and 6ML for platinum capping. The latter result contrasts with the (100) interface, where platinum capping increases tc beyond the bare interface. The observed threshold for conductivity for the bare and the metal-capped interfaces is confirmed by our density functional theory calculations. Interestingly, for (111) SrTiO3/LaAlO3/Metal interfaces, conductivity appears concomitantly with superconductivity in contrast with the (100) SrTiO3/LaAlO3/Metal interfaces where tc is smaller than the critical thickness for superconductivity. We attribute this dissimilarity to the different orbital polarization of e'g for the (111) versus dxy for the (001) interface.