Oxygen vacancy induced insulator-metal transition in LaNiO3 thin films

Abstract

The electronic structures of $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ thin films with an oxygen vacancy on a $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrate are investigated using first-principles calculations. We find that the oxygen vacancy induces the insulator-metal transition as the film thickness is increased. For a 1.0-unit-cell-thick $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ film, an insulating state with an energy gap of 1.2 eV is formed as a result of the large exchange and Coulomb interactions between Ni $3d$ orbitals, whereas a negative charge transfer energy causes restoration of the metallic state in films with a 2.0-unit-cell or larger thickness. Thermodynamic study reveals that an oxygen vacancy induced insulating film may be the preferable structure during the initial stage of film deposition. The low calculated formation energy of 0.26 eV for the oxygen vacancy indicates that the nonstoichiometric and insulating film may survive even the annealing process. Finally, work functions for films with various surfaces are discussed.