Phase Transitions in a Two-dimensional Electron System at Oxide Interface with Dual Gate Tuning

The ground state of a two-dimensional (2D) electron system can be controlled by parameters including disorder, carrier density, and magnetic field. Using the conducting channel formed at the LaAlO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ (001) heterointerface, we performed magnetotransport measurements with simultaneous electric field effect gating from both the top epitaxial LaAlO$_{\mathrm{3}}$ layer and the back SrTiO$_{\mathrm{3}}$ (001) substrate. Besides conventional carrier density tuning, the structural asymmetry inherent to the dual-gate device also enables independent modulation of the disorder level in the conduction channel probed through carrier mobility. Under different top and back gate voltages and magnetic field combinations, the interface channel showed strikingly different conducting states including zero resistance (superconductor), saturating small finite resistance (``metal''), and increasing resistance (insulator), when approaching zero temperature. These results provide a unique opportunity for understanding the quantum phase transitions in 2D superconducting systems with continuously tunable parameters.