Origin of Metallic States at Heterointerface between Band Insulators   LaAlO$_3$ and SrTiO$_3$
  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. 
K. Yoshimatsu, R. Yasuhara, H. Kumigashira, and M. Oshima