  The introduction of manganite buffer layers, La7/8Sr1/8MnO3 (LSMO) in
particular, at the metallic interface between SrTiO3 (STO) and another band
insulator suppresses the carrier density of the interfacial two-dimensional
electron gas (2DEG) and improves significantly the electron mobility. However,
the mechanisms underlying the extreme mobility enhancement remain elusive.
Herein, we used 18O isotope exchanged SrTi18O3 as substrates to create 2DEG at
room temperature with and without the LSMO buffer layer. By mapping the oxygen
profile across the interface between STO18 and disordered LaAlO3 or
yttria-stabilized zirconia (YSZ), we provide unambiguous evidence that redox
reactions occur at oxide interfaces even grown at room temperature. Moreover,
the manganite buffer layer not only suppresses the carrier density but also
strongly suppresses the oxygen exchange dynamics of the STO substrate, which
likely prevents the reduction of STO during the formation of the 2DEG. The
underlying mechanism on the enhanced electron mobility at buffered oxide
interfaces is also discussed.
