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We report on the successful fabrication of (111) oriented thin films of pyrochlore iridate Y2Ir2O7 by means of solid phase epitaxy. Essentially, we developed an entirely in situ annealing protocol, which is superior to the conventional ex-situ routine that requires multi-hour annealing to stabilize the proper pyrochlore structure. The morphological quality of the films has been confirmed by x-ray diffraction, reflectivity, and reciprocal space mapping, demonstrating their high crystallinity with a pure pyrochlore phase and an expected epitaxial relation to the substrate. Strikingly, below the magnetic phase transition, the temperature dependence of resistivity shows a power-law behavior with the power exponent of ∼3/2, characteristic of a Weyl semimetal in the presence of impurities and electron–electron correlations. Below 10 K, the magneto-transport measurements reveal the emergence of a non-saturated negative magnetoresistance up to 9 T with a small "valley" around zero field. These findings are further interpreted in relation to the weak anti-localization effect and the non-collinear antiferromagnetic ordering on the Ir sublattice. [ABSTRACT FROM AUTHOR]

We report on the electronic and magnetic properties of a series of [m EuNiO3/p LaNiO3] superlattices (thickness m and/or p = 1 unit cell) epitaxially grown on single crystalline NdGaO3 substrates. The structural symmetry of these films has been investigated by the combination of in-situ reflection high energy electron diffraction and X-ray diffraction measurements. The metal-insulator transition and the magnetic transition temperatures of the short-period superlattices with m ≥ p are modified from the corresponding bulk Eu1–xLaxNiO3 (x = p m + p ) composition. In contrast to the corresponding bulk doped compound with x = 0.67, the [1 EuNiO3/2 LaNiO3] film remains metallic down to at least 2 K without signs of electronic or magnetic transitions. These findings demonstrate the power of the digital synthesis approach to realize electronic and magnetic phases of perovskite nickelates, unattainable in bulk. [ABSTRACT FROM AUTHOR]

High quality (111)-oriented CoCr2O4/Al2O3 heterostructures were synthesized on the sapphire (0001) single crystal substrates by pulsed laser deposition. The structural properties are demonstrated by in-situ reflection high energy electron diffraction, atomic force microscopy, X-ray reflectivity, and X-ray diffraction. X-ray photoemission spectroscopy confirms that the films possess the proper chemical stoichiometry. This work offers a pathway to fabricating spinel type artificial quasi-two-dimensional frustrated lattices by means of geometrical engineering. [ABSTRACT FROM AUTHOR]

We address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the hetero-interface exemplified by the growth of a correlated metal LaNiO3 on the band insulator SrTiO3 along the pseudo cubic [111] direction. While in general the metallic LaNiO3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, and synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La2Ni2O5 (Ni2+ ) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO3/SrTiO3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface. [ABSTRACT FROM AUTHOR]

We report on the fabrication of all perovskite Mott insulator/band insulator YTiO3/CaTiO3 superlattices by pulsed laser deposition. The combination of in situ reflection high energy electron diffraction, X-ray diffraction, and X-ray reflectivity confirms the high quality of the films grown in a layer-by-layer mode. Electrical transport measurements reveal that a non-SrTiO3 based twodimensional electron gas system has formed at the YTiO3/CaTiO3 interface. These studies offer another route in the pursuit of complex oxide two-dimensional electron gas systems, which allows to obtain greater insights into the exotic many-body phenomena at such interfaces. [ABSTRACT FROM AUTHOR]

The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by the reconstructions at the interface that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO3/mLaAlO3 pseudo cubic (111) superlattices on polar (111)-oriented LaAlO3, the proposed complex oxide candidate for a topological insulating behavior. Comprehensive X-Ray diffraction measurements, reflection high energy electron diffraction, and element specific resonant X-ray absorption spectroscopy affirm their high structural and chemical quality. The study offers an opportunity to fabricate interesting interface and topology controlled (111)-oriented superlattices based on ortho-nickelates. [ABSTRACT FROM AUTHOR]

We have synthesized epitaxial NdNiO3 ultrathin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO3 (001) and LaAlO3 (001), respectively. A combination of x-ray diffraction, temperature dependent resistivity, and soft x-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bulk NdNiO3, the metal-insulator transition under compressive strain is found to be completely quenched, while the transition remains under the tensile strain albeit modified from the bulk behavior. [ABSTRACT FROM AUTHOR]

We have synthesized epitaxial NdNiO3 ultrathin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO3 (001) and LaAlO3 (001), respectively. A combination of x-ray diffraction, temperature dependent resistivity, and soft x-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bulk NdNiO3, the metal-insulator transition under compressive strain is found to be completely quenched, while the transition remains under the tensile strain albeit modified from the bulk behavior. [ABSTRACT FROM AUTHOR]

By using an alternative wet-etch procedure, we have obtained high-quality atomically flat TiO2 terminated surfaces of SrTiO3 single crystals with the morphology equivalent to that of the conventional wet-etch methods. By applying a combined power of photoluminescence (PL) spectroscopy, reflection high-energy electron diffraction, atomic force microscopy imaging, and soft x-ray absorption (XAS), we were able to identify and monitor the complex evolution of oxygen defect states and Ti valency at the surface and near-surface layers. Our experiments revealed a high level of local defects resulting in the presence of the Ti3+ states at the surface. We have developed a method to control the defect states capable of a marked reduction of the defect concentration. We have demonstrated that the PL and XAS are able to distinguish the surface-related Ti3+ states from oxygen vacancies trapping charge transfer vibronic excitons that define the PL intensity. The experimental findings will have important implications for the growth of high-quality ultrathin complex oxide heterostructures. [ABSTRACT FROM AUTHOR]