Origin of Metallic States at Heterointerface between Band Insulators LaAlO$_3$ and SrTiO$_3$

TL;DR

This study uses photoemission spectroscopy to investigate the electronic structure at LaAlO$_3$/SrTiO$_3$ heterointerfaces, revealing that metallic states arise from long-range carrier accumulation rather than short-range charge transfer.

Contribution

It provides direct experimental evidence clarifying the origin of metallic states at the heterointerface, emphasizing the role of long-range carrier accumulation.

Findings

Notched structure observed on SrTiO$_3$ side due to band bending.

No such structure at insulating interface.

Metallic states originate from long-range carrier accumulation.

Abstract

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.