Since its discovery in 2004, the quasi two-dimensional electron gas (q2DEG) at the LaAlO3/SrTiO3 heterointerface has been a paradigm system in studying the emergent phenomena at the oxide interface. Here, I present two unusual ways to tune the q2DEG from LaAlO3 surface, which are intriguing in that surface modification remotely toggles a proximate interface. First, the q2DEG can be locally tuned by using biased atomic force microscope probe [1]. Our studies show that this is caused by the accumulation of charge on the LaAlO3 surface [2, 3]. Second, we found that the q2DEG can be dramatically tuned by surface adsorption of common polar solvents such as acetone, ethanol and water [4]. This strong surface-interface coupling provides deep insight to the origin of the q2DEG. Most significantly, adsorbates induce an insulator to metal transition when the thickness of the LaAlO3 is 3 unit cells, suggesting sensor applications with extremely large sensitivity. Furthermore, by optimizing these two surface controls of LaAlO3, we enhance the Hall mobility of the q2DEG to >20,000 cm2V-1s-1 [5]. This progress provide us a chance to clearly study the quantum transport of the q2DEG, where we observed novel plateaus in Hall conductivity, for the first time in d-electron system [6]. These plateaus have apparent 4-fold degeneracy, suggesting a magnetic break-down transition at the Fermi surface.
