Emergent phenomena in Mott/band insulator heterostructures

The discovery of a two dimensional electron gas (2DEG) at the interface of two insulating oxides (such as LaAlO3/SrTiO 3) has attracted a significant amount of attention for novel oxide based electronics and fundamental physics studies. While most studies have been focused on LaAlO3/SrTiO3 heterostructures less attention has been given to other material systems. Here, we present recent results on a different material system, GdTiO3/SrTiO3. GdTiO 3 is a ferrimagnetic Mott insulator with a polar (001)c surface, while SrTiO3 is a band insulator with a non-polar (001) surface. In this study, GdTiO3 and SrTiO3 layers were grown by hybrid molecular beam epitaxy. Electrical measurements showed the formation of a two-dimensional electron gas (2DEG) at the GdTiO3/SrTiO 3 interface with total sheet carrier density of ~ 3x10 14 cm-2 per interface. The staggered band alignment between GdTiO3 and SrTiO3 causes the 2DEG to be located on the SrTiO3 side of the interface. Shubnikov-de Haas oscillations of the longitudinal resistance in a quantizing magnetic field were observed, indicating two-dimensionality of the electron gas. Ferromagnetic behavior was observed in both GdTiO3/SrTiO3 (where SrTiO 3 is doped by the interface) and La-doped SrTiO3 systems. We also discuss electron correlation effects in this system.