  We investigated the electronic structure of the SrTiO$_3$/LaAlO$_3$
superlattice (SL) by resonant soft x-ray scattering. The (003) peak, which is
forbidden for our "ideal" SL structure, was observed at all photon energies,
indicating reconstruction at the interface. From the peak position analyses
taking into account the effects of refraction, we obtained evidence for
electronic reconstruction of Ti 3d and O $2p$ states at the interface. From
reflectivity analyses, we concluded that the AlO$_2$/LaO/TiO$_2$/SrO and the
TiO$_2$/SrO/AlO$_2$/LaO interfaces are quite different, leading to highly
asymmetric properties.
