Top-gating of the two-dimensional electron gas at complex oxide interfaces

The thesis describes the road towards and experiments with top-gating of the two-dimensional electron gas (2DEG) at the interfaces between the complex oxides LaAlO3 and SrTiO3. These two materials are insulators, however their interface is conducting. It has been demonstrated that a back-gate (at a bottom of the substrate) is able to globally tune the properties of the 2DEG. In this work top-gating is used, since this technique allows for local control over the electron gas, since the top-gate is very close (less than 5 nm) to the electron gas. The work describe in the thesis shows that using e-beam evaporated gold as top-gate electrode leads to low leakage currents. This enables to apply a voltage to the gate to create an electric field across the LaAlO3 layer. Thereby it is possible to switch the conductivity of the 2DEG from conducting to insulating at room temperature. At low temperatures (T = 2 K) the mobility and the carrier density can be tuned. From magnetoresistance measurements at this temperature the spin-orbit coupling has been calculated and it is shown that this depends on the applied gate voltage to the top-gate. At temperatures between 37 mK and 250 mK the electron gas is superconducting. By applying a gate voltage it is possible to manipulate the critical temperature and critical current of the superconductivity.