(111) Oriented 2D Electron Gases and Gate Effect on Shubnikov de-Haas Oscillation Frequency*

The discovery of 2D electron gases (2DEG) at SrTiO₃ surfaces and interfaces has provided a robust platform to study many fundamental phenomena. In (111) oriented SrTiO₃, Dirac bands and charge-ordered insulating phases have been predicted due to the honeycomb lattice formed by the top two layers of TiO₆, similar to graphene. Previously, we have observed Shubnikov-de Haas oscillations to the lowest Landau level at relatively low magnetic field. Here, we report in-situ measurements of the conducing interface formation between amorphous oxide materials on (111) oriented SrTiO₃. Initially, the surface is insulating, but after reaching a critical thickness, the interface becomes conducting and saturates at a larger thickness. At low temperatures, the sample has very high mobilities (>20,000 cm²V^-1s^-1) which is much higher than that of epitaxial interfaces with LaAlO₃ grown at high temperature, possibly due to unstrained structure. Differences in the SdH oscillation frequencies were found in the sample with the same carrier density between virgin samples and those tuned with a back gate. Additionally, after reaching the quantum limit field the sample changes from a metallic state to an insulating state at higher magnetic fields. We are currently investigating the effect of both a back and a top gate on the Shubnikov de-Haas oscillation frequency and the high field insulating state, the result of which will be presented.