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Nature of the metal-insulator transition in few-unit-cell-thick LaNiO3 films.

  • Author(s): Golalikhani, M;
  • Lei, Q;
  • Chandrasena, RU;
  • Kasaei, L;
  • Park, H;
  • Bai, J;
  • Orgiani, P;
  • Ciston, J;
  • Sterbinsky, GE;
  • Arena, DA;
  • Shafer, P;
  • Arenholz, E;
  • Davidson, BA;
  • Millis, AJ;
  • Gray, AX;
  • Xi, XX
  • et al.
Abstract

The nature of the metal-insulator transition in thin films and superlattices of LaNiO3 only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate-film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO3 films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO3 substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO2 termination). Electronic structure measurements using X-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal-insulator transition.

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