Effect of stoichiometry on the interface conductivity of MBE-grown LaAlO$_{3}$/SrTiO$_{3}$ heterostructures

Through careful control of the stoichiometry in molecular-beam epitaxy grown LaAlO$_{3}$/SrTiO$_{3}$ samples, we find that a 2-dimensional electron gas occurs at the interface between the two insulating oxides as reported in samples grown by pulsed-laser deposition. In this talk, I will discuss the controlled experiments that we have carried out, which effectively eliminate the extrinsic effects that have been suggested as possible mechanisms of conductivity, for the conductivity observed in our MBE-grown samples. We find that the cation stoichiometry of the La$_{(1-x)}$Al$_{(1+x)}$O$_{3}$ layer is key to the existence of the interface 2-dimensional electron gas and that a La/Al ratio, (1-x)/(1+x) less than or equal to 0.97 $\pm $ 0.03 is a necessary condition to obtain a conducting interface in this system.