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

The single-crystal SrTiO (001) has two different surface terminations, TiO and SrO. One most remarkable observation in previous studies is that only the heterointerfaces with TiO-terminated SrTiO, which usually combines with polar oxides such as LaAlO, host an electron gas. Here we show that a robust electron gas can be generated between a non-polar oxide, CaHfO, and SrTiO (001) with either termination. Unlike the well-known electron gas of LaAlO/SrTiO, the present one of CaHfO/SrTiO essentially has no critical thickness of CaHfO, 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 CaHfO, field-effect devices are demonstrated using CaHfO/SrTiO 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.