Competing conduction mechanisms for two-dimensional electron gas at LaTiO₃/SrTiO₃ heterointerfaces

In pursuit of understanding the mechanism of two-dimensional electron gas (2DEG), artificial heterostructures based on SrTiO₃ have sparked a wealth of exciting experimental and theoretical results. However, to date, the physical origin of this phenomenon still remains controversial. In our endeavor to unravel the mystery, we have synthesized a series of LaTiO_3+δ/SrTiO₃ films by controlling growth temperature and oxygen pressure, respectively. X-ray absorption results identify the transition of Ti ions from Ti³⁺ to Ti⁴⁺. It is proved that electrical transport properties in the LaTiO₃/SrTiO₃ film are dominated by oxygen vacancies in SrTiO₃. In addition, the metallic behavior observed in the amorphous LaTiO₃/SrTiO₃ film suggests contributions from growth-induced donor defects to 2DEG. Our work presents direct evidence of competing conduction mechanisms for the observed 2DEG at the LaTiO₃/SrTiO₃ interface and highlights the important role of oxygen diffusion from the substrate SrTiO₃. Meanwhile, we emphasize the significance of LaTiO₃ as an oxygen scale meter to investigate interfacial properties of oxide heterostructures.