Structural and transport properties of highly Ru-deficient SrRu0.7O3 thin films prepared by molecular beam epitaxy: comparison with stoichiometric SrRuO3

TL;DR

This study explores how Ru vacancies affect the structural, magnetic, and transport properties of SrRuO3 thin films, revealing that high Ru deficiency still allows metallic conduction and highlighting the importance of stoichiometry control for potential Weyl semimetal applications.

Contribution

It provides detailed analysis of Ru-deficient SrRuO3 thin films, showing their structural integrity and transport behavior despite high Ru vacancies, and compares them with stoichiometric SrRuO3.

Findings

Ru vacancies dominate electrical and magnetic properties for films thicker than 5-10 nm.

SrRu0.7O3 remains metallic despite 30% Ru deficiency.

Weyl fermion transport not observed in Ru-deficient films.

Abstract

We investigate structural and transport properties of highly Ru-deficient SrRu0.7O3 thin films prepared by molecular beam epitaxy on (001) SrTiO3 substrates. To distinguish the influence of the two types of disorders in the films, Ru vacancies within lattices and disorders near the interface, SrRu0.7O3 thin films with various thicknesses (t = 1-60 nm) were prepared. It was found that the influence of the former dominates the electrical and magnetic properties when t > 5-10 nm, while that of the latter does when t < 5-10 nm. Structural characterizations revealed that the crystallinity, in terms of the Sr and O sublattices, of SrRu0.7O3 thin films, is as high as that of the ultrahigh-quality SrRuO3 ones. The Curie temperature (TC) analysis elucidated that SrRu0.7O3 (TC = 140 K) is a material distinct from SrRuO3 (TC = 150 K). Despite the large Ru deficiency (30%), the SrRu0.7O3 films showed metallic conduction when t > 5 nm. In high-field magnetoresistance measurements, the fascinating phenomenon of Weyl fermion transport was not observed for the SrRu0.7O3 thin films irrespective of thickness, which is in contrast to the stoichiometric SrRuO3 films. The (magneto)transport properties suggest that a picture of carrier scattering due to the Ru vacancies is appropriate for SrRu0.7O3, and also that proper stoichiometry control is a prerequisite to utilizing the full potential of SrRuO3 as a magnetic Weyl semimetal and two-dimensional spin-polarized system. Nevertheless, the large tolerance in Ru composition (30 %) to metallic conduction is advantageous for some practical applications where SrRu1-xO3 is exploited as an epitaxial conducting layer.