Photoemission study of polycrystalline Gd_{1-x}Sr_xTiO_{3+delta}: correlation and surface effects

TL;DR

This study investigates the electronic structure of Sr-doped GdTiO3+delta using photoemission, revealing surface inhomogeneity and challenging assumptions about doping effects on the Hubbard bands.

Contribution

It provides new insights into surface effects and doping in polycrystalline Gd_{1-x}Sr_xTiO_{3+delta}, highlighting challenges in interpreting photoemission data.

Findings

Hubbard-model-type two-peak structure observed near Fermi level

Lower Hubbard band energy remains unchanged with doping

Surface doping inhomogeneity affects spectral interpretation

Abstract

We report photoemission studies of polycrystalline samples of Sr-doped GdTiO_{3+delta}, which undergoes a Mott-Hubbard-like metal-insulator transition at a Ti-concentration of about 20%. The Ti 3d-derived valence band near the Fermi level displays a two-peak structure consistent with a Hubbard-model-type interpretation as quasiparticle and lower Hubbard band. Contrary to the theoretical expectation the lower Hubbard band does not change its energy with doping. However, the analysis of the core level spectra and elemental mapping with a scanning electron microscope indicate a strongly inhomogeneous doping concentration in the probed surface regions. This questions the intrinsic character of the valence band spectra and demonstrates a general difficulty when using polycrystalline samples for such studies.