A Laser‐ARPES view of the 2D electron systems at LaAlO_3 /SrTiO_3 and Al/SrTiO_3 interfaces

Abstract

The electronic structure of the two-dimensional electron system (2DES) found at the Al/SrTiO_3 (Al/STO) and LaAlO_3/SrTiO_3 (LAO/STO) interfaces is measured by means of laser angle resolved photoemission spectroscopy, taking advantage of the large photoelectron escape depth at low photon energy to probe these buried interfaces. The possibility of tuning the electronic density in Al/STO by varying the Al layer thickness is demonstrated, and it is shown that the electronic structure evolution is well described by self-consistent tight binding supercell calculations, but differs qualitatively from a rigid band shift model. It is shown that both 2DES are strongly coupled to longitudinal optical phonons, in agreement with previous reports of a polaronic ground state in similar STO based 2DESs. Tuning the electronic density in Al/STO to match that of LAO/STO and comparing both systems, it is estimated that the intrinsic LAO/STO 2DES has a bare band width of approximate to 60 meV and a carrier density of approximate to 6 x 10^13 cm^-2.