Effect of Stoichiometry on the Two-Dimensional Electron Gas at the LaAlO$_{3}$/SrTiO$_{3}$ Interface Grown by MBE.

The discovery of a quasi 2-dimensional electron gas (q2-DEG) at the interface between SrTiO$_{3}$ and LaAlO$_{3}$ has enabled a number of exciting developments. So far this q2-DEG has been observed only in films grown by pulsed-laser deposition, which raised a question as to whether this manifestation has a connection with defects that result from the dynamics of the growth scheme employed. We find that a q2-DEG can also be obtained using the more gentle growth technique, molecular-beam epitaxy, and that control of the stoichiometry of the LaAlO$_{3}$ layer is key to its existence. Small changes in the composition of the LaAlO$_{3}$ layer affect the conductivity at the heterointerface. With appropriate stoichiometry the electron gas transitions into a superconducting state below $\sim $200 mK. Interesting possibilities that stem from these findings of composition control on conductivity and the ability to obtain this q2-DEG under the framework of molecular-beam epitaxy will be discussed.