Electronic charges and electric potential at LaAlO3/SrTiO3 interfaces studied by core-level photoemission spectroscopy

TL;DR

This study uses core-level photoemission spectroscopy to analyze how LaAlO3 thickness affects electronic charges and potential at LaAlO3/SrTiO3 interfaces, revealing charge transfer mechanisms beyond the polar catastrophe model.

Contribution

It provides new insights into charge transfer and interface properties at LaAlO3/SrTiO3 interfaces, highlighting the role of surface defects and adsorbates in charge accumulation.

Findings

Ti3+ signals increase with LaAlO3 thickness in conducting interfaces

Core-level shifts are smaller than polar catastrophe predictions

Charge transfer occurs below the critical thickness due to surface defects

Abstract

We studied LaAlO3/SrTiO3 interfaces for varying LaAlO3 thickness by core-level photoemission spectroscopy. In Ti 2p spectra for conducting "n-type" interfaces, Ti3+ signals appeared, which were absent for insulating "p-type" interfaces. The Ti3+ signals increased with LaAlO3 thickness, but started well below the critical thickness of 4 unit cells for metallic transport. Core-level shifts with LaAlO3 thickness were much smaller than predicted by the polar catastrophe model. We attribute these observations to surface defects/adsorbates providing charges to the interface even below the critical thickness.