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Lippmaa Group

Research Associate

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The ability to grow atomically flat oxide thin films by laser molecular beam epitaxy allows us to study the transport behavior of carriers accumulated in two-dimensional layers at delta-doped interfaces. Fig. 1 shows examples of such heterostructures where a single or double layer of LaTiO3 was grown on a SrTiO3 and capped with another SrTiO3 layer. Each La atom donates an extra electron, some of which will dope the adjacent SrTiO3 layers by charge transfer. We find that multiple electron populations form in this structure, with some electrons localized at the interface, some forming a metallic quantum well, and some spreading deep into the substrate. The relative sizes of these different populations can be tuned by adjusting the total La number in the doping layer, by utilizing surface depletion, or using electrostatic gating. We can observe distinct changes in the magnetotransport behavior when the relative electron population sizes change, as illustrated in Fig. 2, which shows the variation of in-plane magnetoresistance when the carrier number is changed.

Fig. 1. Delta-doped SrTiO3 heterostructures where the number of doped carriers is controlled by the number of (La,Sr)O layers in the titanate lattice.
Fig. 2. In-plane magnetoresistance, measured with the magnetic field parallel to the current flow, for heterostructures doped by 1, 2, or 5 LaO atomic layers in the titanate lattice.

Research Subjects

  1. Growth of thin oxide films and heterostructures by pulsed laser deposition
  2. Development of oxide photoelectrode materials for photocatalytic water splitting
  3. Synthesis of nanostructures and nanocomposite thin films
  4. Development of novel organic – inorganic interfaces