Structure characterization and magneto-transport property of untwinned SrRuO₃ thin films with different thicknesses

The growth of SrRuO₃ (SRO) film with a low defect level is challenging due to the volatility of ruthenium oxide, where significant Ru vacancies can appear in SRO films and thus give rise to a high residual resistivity at low temperatures. To overcome this issue, excess Ru flux was supplied and followed by an adsorption-controlled growth of SRO on a substrate, where the film’s stoichiometry can be thermodynamically self-regulated. We found that the growth condition of initial SrO layer on a TiO₂ terminated SrTiO₃ (STO) (001) substrate is crucial for achieving a low residual resistivity in SRO films grown by adsorption-controlled growth technique, where a c(2x2) superstructure for the optimum initial SrO layer was revealed by the low energy electron diffractions. By using a miscut STO substrate of about 0.1 degrees for the growth of SRO (t-nm)/STO (001) thin films, the volume fraction for the dominant orthorhombic domain can be increased significantly to achieve a nearly single-domain and thus untwinned structure, and it equals ~ 92% for t = 13.7 nm, which was determined from the X-ray azimuthal scan across SRO (02±1)_o reflection. A series of untwinned films with the thickness (t) ranging from 7.7 to 35.3 nm were then grown with a low residual resistivity going from 12.3 to 3.2 μΩcm at 2.5 K, where pronounced quantum oscillations in resistivity can be observed at low temperatures. On the other hand, a crossover from positive magnetoresistance to negative magnetoresistance was found when the magnetic field is gradually tilting along the current direction. All those results support for SRO thin films as an ideal platform for the study of thickness-dependent transport signatures in a topological Weyl metal system.