Rashba splitting in polar-nonpolar sandwich heterostructure: a DFT study

In this study, we employ density functional theory based first-principles calculations to investigate the spin-orbit effects in the electronic structure of a polar-nonpolar sandwich heterostructure namelyLaAlO3/SrTiO3/LaAlO3. Our focus on theTi-3dbands reveals an inverted ordering of theSrTiO3-t2gorbital near the n-type interface, which is consistent with earlier experimental work. In contrast, toward the p-type interface, the orbital ordering aligns with the natural ordering ofSrTiO3orbitals, influenced by crystal field splitting. In the presence of SOC, a notable inter-orbital coupling betweent2gandegorbitals is observed within the tetragonal slab, a phenomenon not reported before in theSrTiO3-based 2D systems. Additionally, our observations highlight that the cubic Rashba splitting in this system surpasses the linear Rashba splitting, contrary to experimental findings. This comprehensive analysis contributes to a refined understanding of the role of orbital mixing in Rashba splitting in the sandwich oxide heterostructures.

Chemical-bond effect on epitaxial strain in perovskite sodium niobate

Epitaxial films and heterostructures of perovskite oxides attract tremendous scientific interest because of the unique phenomena therein. Especially important is the epitaxial growth of films subjected to substrate-induced misfit strain. We show here that in contrast to conventional misfit-controlled epitaxy, chemical bonds determine the crystal stability and strain in epitaxial films of sodium niobate on different cubic substrates. Strain relaxation in sodium niobate is independent of misfit magnitude and proceeds through perovskite-specific tilting of oxygen octahedra in addition to common defect formation. The observed structural relaxation evidences a major role of a large internal strain that originates from chemical bonds in the perovskite cell. The effect of chemical bonds on film strain is anticipated to also control the epitaxy of other perovskite oxides and related compounds.