  The discovery of two-dimensional electron gases (2DEGs) at the
heterointerface between two insulating perovskite-type oxides, such as LaAlO3
and SrTiO3, provides opportunities for a new generation of all-oxide electronic
and photonic devices. However, significant improvement of the interfacial
electron mobility beyond the current value of approximately 1,000 cm2V-1s-1 (at
low temperatures), remains a key challenge for fundamental as well as applied
research of complex oxides. Here, we present a new type of 2DEG created at the
heterointerface between SrTiO3 and a spinel {\gamma}-Al2O3 epitaxial film with
excellent quality and compatible oxygen ions sublattices. This
spinel/perovskite oxide heterointerface exhibits electron mobilities more than
one order of magnitude higher than those of perovskite/perovskite oxide
interfaces, and demonstrates unambiguous two-dimensional conduction character
as revealed by the observation of quantum magnetoresistance oscillations.
Furthermore, we find that the spinel/perovskite 2DEG results from
interface-stabilized oxygen vacancies and is confined within a layer of 0.9 nm
in proximity to the heterointerface. Our findings pave the way for studies of
mesoscopic physics with complex oxides and design of high-mobility all-oxide
electronic devices.
