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 by 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 happens for tensile strain. Structural analyses reveal that the electronic transition accompanies a structural phase transition restoring inversion symmetry, and the strain compresses the interfacial oxygen octahedra of Ti and thus makes the d energy level 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 structural and electronic properties of such oxide superlattices and heterostructures.