Strain-controlled Insulator-Metal Transition in YTiO3/SrTiO3 Superlattices: A First-Principles Study

The structural, magnetic, and electronic properties of (STO)4/(YTO)2 superlattice consisting of Mott insulator YTiO3 (YTO) and band insulator SrTiO3 (STO) under strain are investigated by the density-functional-theory plus U method. It is found that an insulator-metal transition occurs when a compressive strain of 0.2% is applied. The structural analyses reveal that the presence of metallic state in such superlattices accompanies structural phase transition with restoring of inversion symmetry. Further study shows that this strain-induced structural transition makes the d energy level of the interfacial Ti atoms of the YTO layer move upward due to the decreasing of the TiO6 octahedral volume and induces the electron reconstruction in the whole superlattice systems. In addition, when the on-site interaction U is changed from 5 to 4 eV, a similar insulator-metal transition also occurs in such superlattices due to the weakened electron correlation. These findings can improve our understanding of the insulator-metal transitions in such oxide superlattices.