  In recent years, striking discoveries have revealed that two-dimensional
electron liquids (2DEL) confined at the interface between oxide band-insulators
can be engineered to display a high mobility transport. The recognition that
only few interfaces appear to suit hosting 2DEL is intriguing and challenges
the understanding of these emerging properties not existing in bulk. Indeed,
only the neutral TiO2 surface of (001)SrTiO3 has been shown to sustain 2DEL. We
show that this restriction can be surpassed: (110) and (111) surfaces of SrTiO3
interfaced with epitaxial LaAlO3 layers, above a critical thickness, display
2DEL transport with mobilities similar to those of (001)SrTiO3. Moreover we
show that epitaxial interfaces are not a prerequisite: conducting (110)
interfaces with amorphous LaAlO3 and other oxides can also be prepared. These
findings open a new perspective both for materials research and for elucidating
the ultimate microscopic mechanism of carrier doping.
