  The observation of a two dimensional electron gas (2DEG) (1, 2),
superconductivity (3, 4), magnetic effects (5) and electronic phase separation
(6-8) at the interfaces of insulating oxides, especially LaAlO3/SrTiO3, has
further enhanced the potential of complex oxides for novel electronics. The
occurrence of the 2DEG is strongly believed to be driven by the polarization
discontinuity (9) at the interface between the two oxides. In this scenario,
the crystal orientation plays an important role and no conductivity would be
expected for e.g., the interface between LaAlO3 and (110)-oriented SrTiO3,
which should not have a polarization discontinuity (10, 11). Here, we report
the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface
prepared on (110)-oriented SrTiO3. The conductivity was further found to be
strongly anisotropic, with the ratio of the conductance along the different
directions parallel to the substrate surface showing a remarkable dependence on
the oxygen pressure during deposition. The conductance and its anisotropy are
discussed based on the atomic structure at the interface, as revealed by
Scanning Transmission Electron Microscopy (STEM) and further supported by
density functional theory (DFT) calculations.
