Strain-controlled insulator–metal transition in YTiO3/SrTiO3 superlattices: effect of interfacial reconstruction

The structural, magnetic, and electronic properties of short-period STO/YTO superlattices consisting of Mott insulator YTiO3 (YTO) and band insulator SrTiO3 (STO) are investigated using the density-functional-theory plus U method. It is found that an insulator–metal transition occurs when a compressive strain is applied, and no transition occurs for tensile strain. Structural analyses reveal that the electronic transition accompanies a structural phase transition, restoring the inversion symmetry, and the strain compresses the interfacial oxygen octahedra of Ti and thus makes the d energy levels of the interfacial Ti atoms move upward so as to induce electron transfer to the STO layer. This mechanism is supported by the fact that a similar insulator–metal transition also occurs when the on-site U is reduced. These findings can improve our understanding of the structural and electronic properties of such oxide superlattices and heterostructures.