Distinct differences in surface transport between electrolyte-gated (110) and (001) SrTiO3

Electrolyte gating technology has been widely used as an effective tool to study novel physics at complex oxide surfaces and interfaces. Certain emergent phenomena reported in electro-gated SrTiO3 (STO) surfaces are particularly interesting. Here, we report on the disparate electron transport behaviors of electrolyte-gated STO (001) and (110) oriented surfaces. In contrast to the anomalous transport from an insulating state to a Kondo-like state and then metallic states on the (001) surface, with increasing carrier density, the (110) surface always behaves as an insulating state. A comparison study suggests that the oxygen vacancies and localized Ti3+ ions on the (001) surface are scatter carriers, but no such defects are found on the (110) surface. This suggests that these surfaces are intrinsically insulating, and the observed anomalous effects are likely induced by the Ti3+ ions and oxygen vacancies introduced during electrolyte gating. This work sheds light on complicated phenomena in electrolyte-gated STO-based systems.