  We have studied the electronic structure at the heterointerface between the
band insulators LaAlO$_3$ and SrTiO$_3$ using $in situ$ photoemission
spectroscopy. Our experimental results clearly reveal the formation of a
notched structure on the SrTiO$_3$ side due to band bending at the metallic
LaAlO$_3$/TiO$_2$-SrTiO$_3$ interface. The structure, however, is absent at the
insulating LaAlO$_3$/SrO-SrTiO$_3$ interface. The present results indicate that
the metallic states originate not from the charge transfer through the
interface on a short-range scale but from the accumulation of carriers on a
long-range scale.
