A termination-insensitive and robust electron gas at the heterointerface of two complex oxides

The single-crystal SrTiO₃ (001) has two different surface terminations, TiO₂ and SrO. One most remarkable observation in previous studies is that only the heterointerfaces with TiO₂-terminated SrTiO₃, which usually combines with polar oxides such as LaAlO₃, host an electron gas. Here we show that a robust electron gas can be generated between a non-polar oxide, CaHfO₃, and SrTiO₃ (001) with either termination. Unlike the well-known electron gas of LaAlO₃/SrTiO₃, the present one of CaHfO₃/SrTiO₃ essentially has no critical thickness of CaHfO₃, can survive a long-time oxygen annealing at high temperature, and its transport properties are stable under exposure to water and other polar solvents. By electrostatic gating through CaHfO₃, field-effect devices are demonstrated using CaHfO₃/SrTiO₃ heterointerfaces with both terminations. These results show that the electron gas reported in the present study is unique and promising for applications in oxide electronics.