SrTiO3 interface in the (111) orientation have recently attracted special interest owing to a combination of hexagonal crystal symmetry, strongly correlated d-orbital electrons, and large spin-orbit coupling effect. We have created two-dimensional (2D) electron liquid at SrTiO3 interface with high mobility (>20,000 cm2V-1s-1) and controllable carrier density. We observe the Shubnikov-de Haas oscillations into the quantum limit at high magnetic fields up to 35 T and low temperatures down to 300 mK at SrTiO3 (111) interface. Beyond the quantum limit, the magnetoresistance exhibits a linear field dependence behavior with an insulating temperature dependence, reflecting the strongly correlated nature of the 2D electron liquid at SrTiO3 (111) interface. Angular dependent spin splitting is observed at low Landau levels which is attributed to the interplay between the Zeeman splitting and Rashba spin-orbit coupling according to our theoretical modeling. The occurrence of spin-orbit coupling effect at SrTiO3 (111) interface is further supported by the coexistence of negative in-plane magnetoresistance, anomalous Hall effect and second harmonic bilinear magnetoresistance. 

In the exploration of the interplay between superconductivity and spin-orbit coupling 2D electron liquid, we have fabricated and measured the side tunneling junctions between Nb leads and 2D electron systems at SrTiO3/SiO2 interfaces. We demonstrate that the junction resistance can be effectively decreased by slight 45-deg ion milling at the junction area. The typical tunneling spectra exhibit clear superconducting gap of Nb superimposed on the asymmetric background. The side tunneling spectra are studied in both (001) and (111) oriented SrTiO3 interface. To have a clear picture on the asymmetric background, we have also studied the side tunneling behavior between Au leads and 2D electron systems at SrTiO3/SiO2 interfaces. The spectra shed lights on the charge distribution in 2D electron system at the SrTiO3 interface. Particularly, an insulating gap opens up with decreasing carrier density where the system undergoes a metallic to insulating transition.