  Electric field effect in electronic double layer transistor (EDLT)
configuration with ionic liquids as the dielectric materials is a powerful
means of exploring various properties in different materials. Here we
demonstrate the modulation of electrical transport properties and extremely
high mobility of two-dimensional electron gas at LaAlO$_3$/SrTiO$_3$ (LAO/STO)
interface through ionic liquid-assisted electric field effect. By changing the
gate voltages, the depletion of charge carrier and the resultant enhancement of
electron mobility up to 19380 cm$^2$/Vs are realized, leading to quantum
oscillations of the conductivity at the LAO/STO interface. The present results
suggest that high-mobility oxide interfaces which exhibit quantum phenomena
could be obtained by ionic liquid-assisted field effect.
