Ferroelectric Modulation of Two-dimensional Electron Gas Conductivity at Oxide Interfaces

In this report, by inserting a ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_{3}$ layer between LaAlO$_{3}$/SrTiO$_{3}$ heterostructure, a two-dimensional electron gas (2DEG) was found at LaAlO$_{3}$/ Ba$_{0.2}$Sr$_{0.8}$TiO$_{3\, }$interface. With electrical, optical, piezoresponse force microscopic measurements and first-principle calculations, we studied the impact of this ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_{3\, }$layer on the 2DEG. Both carrier density and mobility of the 2DEG can be modulated by changing the thickness of the ferroelectric layer. We also observed that Ba$_{0.2}$Sr$_{0.8}$TiO$_{3}$ layer can suppress oxygen vacancy formation, leading to observation of temperature-independent polarization-induced carrier density. These results indicate that the 2DEG at oxide interfaces can be ferroelectrically modulated.