A Laser-ARPES View of the 2D Electron Systems at LaAlO3/SrTiO3 and Al/SrTiO3 Interfaces

TL;DR

This study uses laser ARPES to investigate the electronic structures of 2D electron systems at Al/SrTiO3 and LaAlO3/SrTiO3 interfaces, revealing tunable densities, phonon coupling, and detailed electronic properties.

Contribution

It provides new insights into the electronic structure and tunability of 2DES at these interfaces, supported by experimental measurements and theoretical calculations.

Findings

Electronic density in Al/SrTiO3 can be tuned by Al layer thickness.

Both 2DES are strongly coupled to longitudinal optical phonons.

Estimated intrinsic properties of LAO/STO 2DES include a ~60 meV band width and ~6×10^13 cm^-2 carrier density.

Abstract

We have measured the electronic structure of the two-dimensional electron system (2DES) found at the Al/SrTiO3 (Al/STO) and LaAlO3/SrTiO3 (LAO/STO) interfaces 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. We demonstrate the possibility of tuning the electronic density in Al/STO by varying the Al layer thickness and show that the electronic structure evolution is well described by self-consistent tight binding supercell calculations, but differs qualitatively from a rigid band shift model. We show 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, we estimate that the intrinsic LAO/STO 2DES has a bare band width of ~ 60 meV and a carrier density of ~ 6 10^13 cm-2.