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The electronic properties of complex oxide heterostructures are governed by the physics at the interface between the different materials. Here, the authors use infrared ellipsometry and confocal Raman spectroscopy to show the presence of non-collinear and asymmetric interfacial polar moments in SrTiO3-based heterostructures underlying the important role of oxygen vacancies in these systems.

In this study, we investigated the structural and optical properties of Ge-doped SbTe (Ge-ST) thin films with three differing compositions: Ge0.06Sb0.77Te0.17 (Ge-STH), Ge0.05Sb0.70Te0.25 (Ge-STM), and Ge0.05Sb0.64Te0.31 (Ge-STL), grown on Si substrate by radio-frequency sputtering method. The films were annealed at 250°C for crystallization and their crystal structures were examined by X-ray diffraction. Compared to the X-ray diffraction spectra of the undoped SbTe, the Ge-ST thin films had a hexagonal structure with large stacking periods. Using Raman spectroscopy, we investigated the shift of the phonon mode frequencies (A1g and Eg) of the films with varying Sb:Te ratios. We compared the dependence of the phonon frequencies of Ge-ST on the Sb content to those of the corresponding undoped SbTe. The composition dependence of the A1g phonon frequency could be explained in terms of the linear extrapolation of Sb and Sb2Te3 crystals. By using spectroscopic ellipsometry, we measured the dielectric function of the thin films in the near-IR, visible, and ultraviolet spectral regions. The optical energy gaps and bandgaps of the amorphous and crystalline phases, respectively, were determined using linear extrapolation of the absorption coefficient. The optical gap energies of the amorphous Ge-ST films were determined to be about 0.5-0.6 eV, whereas the indirect bandgap energies of the crystalline films shrank substantially to about 0.15-0.2 eV. [ABSTRACT FROM AUTHOR]

Iridates have attracted immense interest since their strong spin–orbit coupling (SOC) can lead to rich exotic phenomena such as a Jeff = ½ Mott insulating state. Here we report a novel iridate discovered in our efforts which aimed to synthesize Ba2IrO4 thin films. Through systematic transmission and scanning transmission electron microscopy studies, we have shown this new compound possesses a layered orthorhombic structure with the composition of Ba7Ir3O13+δ (BIO). This material is an insulator with an optical band gap of ∼1.3 eV. Furthermore, we found that the thin films of this material can be grown on differently orientated perovskite substrates or MgO substrates. Although all these films maintain an identical crystallographic orientation, i.e. its c-axis perpendicular to the substrate surface, they form various domain structures dependent on the substrate. When (001)-oriented LaAlO3 and (111) oriented SrTiO3 perovskites are used as substrates, the domains show 12 fold and 6 fold symmetry respectively, and the domain orientations are highly coherent and the domain-walls are atomically sharp. However, the films on the (110) oriented MgO substrates feature much less coherent domain walls and thread dislocations occur at the domain boundaries. These findings not only reveal a new playground for the study of the novel SOC physics of iridates, but also provide a route to tailor the domain wall structure via epitaxial lattice mismatch in films. [ABSTRACT FROM AUTHOR]