31 research outputs found

    Interface-engineered hole doping in Sr2IrO4/LaNiO3 heterostructure

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    The relativistic Mott insulator Sr2IrO4 driven by large spin-orbit interaction is known for the Jeff = 1/2 antiferromagnetic state which closely resembles the electronic structure of parent compounds of superconducting cuprates. Here, we report the realization of hole-doped Sr2IrO4 by means of interfacial charge transfer in Sr2IrO4/LaNiO3 heterostructures. X-ray photoelectron spectroscopy on Ir 4f edge along with the X-ray absorption spectroscopy at Ni L2 edge confirmed that 5d electrons from Ir sites are transferred onto Ni sites, leading to markedly electronic reconstruction at the interface. Although the Sr2IrO4/LaNiO3 heterostructure remains non-metallic, we reveal that the transport behavior is no longer described by the Mott variable range hopping mode, but by the Efros-Shklovskii model. These findings highlight a powerful utility of interfaces to realize emerging electronic states of the Ruddlesden-Popper phases of Ir-based oxides.Comment: 9 pages including 3 figures and reference

    Orientation-dependent stabilization of MgCr2_2O4_4 spinel thin films

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    AB2_2O4_4 normal spinels with a magnetic B site can host a variety of magnetic and orbital frustrations leading to spin-liquid phases and field-induced phase transitions. Here we report the first epitaxial growth of (111)-oriented MgCr2_2O4_4 thin films. By characterizing the structural and electronic properties of films grown along (001) and (111) directions, the influence of growth orientation has been studied. Despite distinctly different growth modes observed during deposition, the comprehensive characterization reveals no measurable disorder in the cation distribution nor multivalency issue for Cr ions in either orientation. Contrary to a naive expectation, the (111) stabilized films exhibit a smoother surface and a higher degree of crystallinity than (001)-oriented films. The preference in growth orientation is explained within the framework of heteroepitaxial stabilization in connection to a significantly lower (111) surface energy. These findings open broad opportunities in the fabrication of 2D kagome-triangular heterostructures with emergent magnetic behavior inaccessible in bulk crystals

    Epitaxial stabilization of the frustrated Ge-based spinel thin films

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    Frustrated magnets can host numerous exotic many-body quantum and topological phenomena. GeNi2_2O4_4 is a three dimensional S=1S=1 frustrated magnet with an unusual two-stage transition to the two-dimensional antiferromagnetic ground state, while GeCu2_2O4_4 is a high-pressure phase with a strongly tetragonally elongated spinel structure and magnetic lattice formed by S=1/2S=1/2 CuO2_2 linear chains with frustrated exchange interactions and exotic magnetic behavior. Here we report on the first thin-film epitaxial stabilization of these two compounds. Developed growth mode, surface morphology, crystal structure and copper valence state were characterized by in-situ reflection high-energy electron diffraction, atomic force microscopy, X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy and resonant X-ray absorption spectroscopy. Our results pave an alternative route to the comprehensive investigation of the puzzling magnetic properties of these compounds and exploration of novel emergent features driven by strain

    Anomalous orbital structure in two-dimensional titanium dichalcogenides

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    Generally, lattice distortions play a key role in determining the ground states of materials. Although it is well known that trigonal distortions are generic to most two-dimensional transition metal dichalcogenides, the impact of this structural distortion on the electronic structure has not been understood conclusively. Here, by using a combination of polarization dependent X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and atomic multiplet cluster calculations, we have investigated the electronic structure of titanium dichalcogenides TiX2 (X=S, Se, Te), where the magnitude of the trigonal distortion increase monotonically from S to Se and Te. Our results reveal the presence of an anomalous and large crystal filed splitting. This unusual kind of crystal field splitting is likely responsible for the unconventional electronic structure of TiX2 compounds. Our results also indicate the drawback of the distorted crystal field picture in explaining the observed electronic ground state of these materials and emphasize the key importance of metal-ligand hybridization and electronic correlation in defining the electronic structures near Fermi energy

    Synthesis of epitaxial magnetic pyrochlore heterojunctions

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    The synthesis of stoichiometric and epitaxial pyrochlore iridate thin films presents significant challenges yet is critical for unlocking experimental access to novel topological and magnetic states. Towards this goal, we unveil an in-situ two-stage growth mechanism that facilitates the synthesis of high-quality oriented pyrochlore iridate thin films. The growth starts with the deposition of a pyrochlore titanate as an active iso-structural template, followed by the application of an in-situ solid phase epitaxy technique in the second stage to accomplish the formation of single crystalline, large-area films. This novel protocol ensures the preservation of stoichiometry and structural homogeneity, leading to a marked improvement in surface and interface qualities over previously reported methods. The success of this synthesis approach is attributed to the application of directional laser-heat annealing, which effectively reorganizes the continuous random network of ions into a crystalline structure, as evidenced by our comprehensive analysis of the growth kinetics. This new synthesis approach advances our understanding of pyrochlore iridate film fabrication and opens a new perspective for investigating their unique physical properties.Comment: 11 pages, 4 figures; supplementary materials (1 table, 6 figures
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