Dependence of electronic structure of SrRuO3 and the degree of correlation on cation off-stoichiometry

TL;DR

This study investigates how cation off-stoichiometry, specifically ruthenium vacancies, affects the electronic structure and correlation strength in SrRuO3 thin films, revealing that vacancies increase electronic correlation and alter transport properties.

Contribution

It demonstrates controlled growth of SrRuO3 films with varying ruthenium vacancies and links vacancy concentration to changes in electronic structure and correlation effects.

Findings

Ruthenium vacancies increase the unit cell volume.

Higher vacancies lead to increased resistivity and decreased RRR.

Correlation strength increases with ruthenium vacancies, as shown by spectroscopic analysis.

Abstract

We have grown and studied high quality SrRuO3 films grown by MBE as well as PLD. By changing the oxygen activity during deposition we were able to make SrRuO3 samples that were stoichiometric (low oxygen activity) or with ruthenium vacancies (high oxygen activity). Samples with strontium vacancies were found impossible to produce since the ruthenium would precipitate out as RuO2. The volume of the unit cell of SrRuO3 becomes larger as more ruthenium vacancies are introduced. The residual resistivity ratio (RRR) and room temperature resistivity were found to systematically depend on the volume of the unit cell and therefore on the amount of ruthenium vacancies. The RRR varied from ~30 for stoichiometric samples to less than two for samples that were very ruthenium poor. The room temperature resistivity varied from 190 microOhm cm for stoichoimetric samples to over 300 microOhm cm for very ruthenium poor samples. UPS spectra show a shift of weight from the coherent peak to the incoherent peak around the Fermi level when samples have more ruthenium vacancies. Core level XPS spectra of the ruthenium 3d lines show a strong screened part in the case of stoichiometric samples. This screened part disappears when ruthenium vacancies are introduced. Both the UPS and the XPS results are consistent with the view that correlation increases as the amount of ruthenium vacancies increase.