  When insulator LaAlO3 is grown by epitaxy onto a TiO2-terminated {100}
surface of insulator SrTiO3, the resulting system has a metallic character.
This phenomenon has been associated with an electrostatic frustration at the
interface, as {100} surfaces of SrTiO3 are neutral while those of LaAlO3 are
polar, but its microscopic mechanism is not quite understood. Here, we present
a structural characterisation of this interface by aberration-corrected
transmission electron microscopy. The unit cells at the interface appear
elongated: we discuss this distortion in terms of electrostatic charge and
extra carriers at the interface.
