Tailoring a two-dimensional electron gas at the LaAlO$_{3}$/SrTiO$_{3}$ (001) interface by epitaxial strain

Recently a two-dimensional electron gas (2DEG) was discovered at the interface between insulating oxides LaAlO$_{3}$ and SrTiO$_{3}$. Properties of this 2DEG have attracted interest due to its potential applications in nanoelectronics. Control over the carrier density and mobility is essential for applications of these novel systems, and may be achieved by epitaxial strain. The relationship between the strain and electrical properties of this 2DEG remains largely unexplored. We use different lattice constant single crystal substrates to produce LaAlO$_{3}$/SrTiO$_{3}$ interfaces with controlled levels of biaxial epitaxial strain. We have found that tensile strained SrTiO$_{3}$ destroys the conducting 2DEG, while compressively strained SrTiO$_{3}$ retains the 2DEG, but with a carrier concentration reduced in comparison to the unstrained LaAlO$_{3}$/SrTiO$_{3}$ interface. We have also found that the critical LaAlO$_{3}$ overlayer thickness for 2DEG formation increases with SrTiO$_{3}$ compressive strain. Our first-principles calculations suggest that a strain-induced electric polarization in the SrTiO$_{3}$ layer is responsible for this behavior.