Depth profiling electronic structures of LaTiO₃/SrTiO₃ heterostructures using soft X-ray ARPES

As with other transition-metal oxide interfaces, LaTiO₃/SrTiO₃ interfaces exhibit interesting electronic properties, such as a two-dimensional electron gas. While the available Mott states and multiple pathways to metallicity in LaTiO₃ can lead to a variety of applications in oxide electronics, the origin of the different properties remain uncertain. Utilizing real-time, in-situ X-ray diffraction at the synchrotron, robust but thin LaTiO₃/SrTiO₃ heterostructures were fabricated using oxide molecular beam epitaxy. A thickness of six unit-cells was determined to be critical, at which point the LaTiO₃ / SrTiO₃ heterostructures begin to sustain sharp, well-defined interfaces. The layers of LaTiO₃ and SrTiO₃ were sufficiently thin to benefit from the finite escape length of electrons at resonant soft X-ray photoemission, and the heterostructures were transferred in vacuo after growth to another chamber for synchrotron-based X-ray photoemission spectroscopy studies. With the X-ray energy tuned to the Ti-2p resonance, the LaTiO₃/SrTiO₃ interfaces could be probed with enough penetration depth and selectivity. It is shown that all of the heterointerfaces exhibit the 2-dimensional electron gas.