Influence of initial SrO growth on the residual resistivity in epitaxial SrRuO3/SrTiO3 (001) thin films.

Akhilesh Singh^1*, Uddipta Kar¹, Song Yang², Chun-Yen Lin², Chia-Hung Hsu², Wei-Li Lee¹

¹Physics, Academia Sinica, Taipei, Nangang, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Akhilesh Singh, email:drakhintu@gmail.com

Recently, the ferromagnetic oxide SrRuO3 (SRO) emerges as a possible topological Weyl semimetal system. The growth of SRO ultra-thin film with a high crystallinity and low residual resistivity is a challenging issue due to the volatility of the ruthenium oxide. In this work, an adsorption-controlled growth technique was utilized with an oxide molecular beam epitaxy (MBE) system, where the film’s stoichiometry can be thermodynamically self-regulated. We uncovered that the initial growth conditions of SrO layer largely influence the follow-up SRO growth. Using electron diffraction technique, we found that an optimized initial SrO layer on the TiO2 terminated SrTiO3 (STO) substrate gives rise to a c(2 × 2) superstructure, which turned out to be crucial for excellent crystallinity and low residual resistivity in the SRO/STO (001) films. Using the optimum initial SrO growth condition, we grew a series of SRO (t-nm)/STO (001) films. The SRO/STO (001) films exhibit excellent crystallinity with orthorhombic-phase down to t ≈ 4.3 nm, which was confirmed by high-resolution X-ray measurements. From X-ray azimuthal scan across SRO orthorhombic (02 ± 1) reflections, we uncover four structural domains with a dominant domain of orthorhombic SRO [001] along cubic STO [010] direction. The dominant domain population in SRO films depends on t, STO miscut angle, and STO miscut direction. On the other hand, metallic and ferromagnetic properties were well preserved down to t ≈ 1.2 nm. Residual resistivity ratio (RRR = ρ(300K)/ρ(5K)) reduces from 77.1 for t ≈ 28.5 nm to 2.5 for t ≈ 1.2 nm, while ρ(5K) increases from 2.5 μΩcm for t ≈ 28.5 nm to 131.0 cm for t ≈ 1.2 nm. The detailed investigations on the growth and characterization of high-crystallinity SRO/STO (001) films with a single domain will be presented and discussed.

Keywords: thin films, growth of low-dimensional materials, material growth, synthesis, and characteristics, non-Fermi liquid