Thickness-Dependent Perovskite Octahedral Distortions at Heterointerfaces

Fowlie, Jennifer; Lichtensteiger, Céline; Gibert, Marta; Meley, Hugo; Willmott, P. R.; Triscone, Jean‐Marc

doi:10.1021/acs.nanolett.9b01772

Cited by 34 publications

(29 citation statements)

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“…Finally, at 2 u.c., only the characteristic surface structure is retained; it is this distortion that takes dominance toward the atomic limit. These structures are consistent with what was found from synchrotron X‐ray diffraction …”

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confidence: 91%

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Conductivity and Local Structure of LaNiO₃ Thin Films

et al. 2017

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approaches to controlling the MIT have been made, for example, by electric field effects [9] and through optical means. [10] Today, RNOs retain a strong focus, with recent work striving to understand their physics. [11][12][13][14][15] The R = La compound is the only RNO that does not have an MIT in bulk; it is metallic and paramagnetic at all temperatures. LaNiO 3 (LNO) may prove an ideal candidate as a base for engineering functional oxide heterostructures. For instance, it was suggested that specially engineered superlattices, based on single unit cells (u.c.) of LNO, may support superconductivity, [16] and it has been shown that this material is orbitally polarizable in specifically designed heterostructures. [17,18] Necessary to fine-tune the functionalities of LNO is a full understanding of the effects of heterostructuring on an atomic level, and the implications that the local structure, at this scale, has on the electronic properties. A close examination of the thin film structure at the boundaries with the substrate and the vacuum, as well as the effects of reducing the dimensionality on coexistence and, ultimately, competition between these local structures, is required.In reducing dimensionality, three conductivity regimes have previously been observed; thicker metallic films, intermediate thicknesses with a resistivity upturn, and insulating films under the ultrathin limit, which can be 3-6 u.c., depending upon the substrate. [19][20][21] In line with this, photoemission studies found drastic changes to the LNO Fermi surface as the thickness approaches a few u.c., indicating that there is a fundamental change in the electronic structure. [22,23] Here we report an intriguing thickness-dependent transport behavior in high-quality LNO films grown on a (001) LaAlO 3 (LAO) substrate, whereby conductivity is enhanced in films of 6-11 u.c. (2.3-4.3 nm). A maximum conductivity is also observed in ab initio calculations (for a thickness of 6-8 u.c.). In agreement with scanning transmission electron microscopy (STEM), the simulations further indicate that there are three characteristic local structures in the depth of the films. A three-element model of parallel conductors reproduces the thickness-dependent transport behavior well, and implies that conductivity enhancement derives from a struggle for dominance between the local structure of the surface and of the heterointerface.Both LNO and LAO are rhombohedral (R-3c) in bulk. LNO (pseudocubic lattice parameter 3.84 Å) deposited on LAO (pseudocubic lattice parameter 3.79 Å) is compressively strained by −1.3%.A marked conductivity enhancement is reported in 6-11 unit cell LaNiO 3 thin films. A maximal conductivity is also observed in ab initio calculations for films of the same thickness. In agreement with results from state of the art scanning transmission electron microscopy, the calculations also reveal a differentiated film structure comprising characteristic surface, interior, and heterointerface structures. Based on this observation, a three-element para...

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confidence: 91%

“…The full, distorted u.c. of the film and the substrate were taken into account, with the LNO now monoclinic from the strain‐induced symmetry lowering, compared to bulk; the symmetry being the same for all thicknesses . For more details see the Experimental Section and the Supporting Information.…”

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Conductivity and Local Structure of LaNiO₃ Thin Films

et al. 2017

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“…Another minor contribution could be due to the rearrangement of the oxygen atoms at the interface, giving rise to a distortion of the interfacial oxygens' octahedra, yielding an enhanced Dzyaloshinskii-Moriya interaction and, thus, a larger weak ferromagnetic component [45,46]. The oxygen octahedral distortion (OOR) is a consequence not only of the strain imposed by the substrate, but also of the discontinuity present at the interface which changes from a 0 a 0 a 0 (in Glazer's notation) in STO to a − a − c + in CMO, similar to what was found in other heterointerfaces [47][48][49][50][51]. Nonetheless, these distortions might be important only in the first two layers close to the interface, as it was reported in Ref.…”

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confidence: 63%

Strain-induced magnetic transition in CaMnO3 ultrathin films

et al. 2020

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The effect of high tensile strain and low dimensionality on the magnetic and electronic properties of CaMnO 3 ultrathin films, epitaxially grown on SrTiO 3 substrates, are experimentally studied and theoretically analyzed. By means of ab initio calculations, we find that both the high strain produced by the substrate and the presence of the free surface contribute to the stabilization of an in-plane ferromagnetic coupling, giving rise to a nonzero net magnetic moment in the ultrathin films. Coupled with this change in the magnetic order we find an insulatormetal transition triggered by the quantum confinement and the tensile epitaxial strain. Accordingly, our magnetic measurements in 3-nm ultrathin films show a ferromagnetic hysteresis loop, absent in the bulk compound due to its G-type antiferromagnetic structure.

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“…The SNO-based nanodevices studied here consist of a 150 nm thick SNO film epitaxially grown with a high vacuum sputtering system on (111) pc -oriented LaAlO 3 substrate [5]. This orientation was chosen such as to be able to access Bragg peaks associated with octahedral distortions of the kind (101) [40][41][42]. Two 5 µm-wide electrodes of Pd and Au were fabricated over the film with a lateral gap of 1 − 2 µm using e-beam lithography.…”

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Proton distribution visualization in perovskite nickelate devices utilizing nanofocused X-rays

Zaluzhnyy,

Sprau,

Tran

et al. 2021

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We use a 30-nm x-ray beam to study the spatially resolved properties of a SmNiO 3 -based nanodevice that is doped with protons. The x-ray absorption spectra supported by density-functional theory (DFT) simulations show partial reduction of nickel valence in the region with high proton concentration, which leads to the insulating behavior. Concurrently, x-ray diffraction reveals only a small lattice distortion in the doped regions. Together, our results directly show that the knob which proton doping modifies is the electronic valency, and not the crystal lattice. The studies are relevant to on-going efforts to disentangle structural and electronic effects across metal-insulator phase transitions in correlated oxides.

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Thickness-Dependent Perovskite Octahedral Distortions at Heterointerfaces

Cited by 34 publications

References 50 publications

Conductivity and Local Structure of LaNiO₃ Thin Films

Conductivity and Local Structure of LaNiO₃ Thin Films

Strain-induced magnetic transition in CaMnO3 ultrathin films

Proton distribution visualization in perovskite nickelate devices utilizing nanofocused X-rays

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Thickness-Dependent Perovskite Octahedral Distortions at Heterointerfaces

Cited by 34 publications

References 50 publications

Conductivity and Local Structure of LaNiO3 Thin Films

Conductivity and Local Structure of LaNiO3 Thin Films

Strain-induced magnetic transition in CaMnO3 ultrathin films

Proton distribution visualization in perovskite nickelate devices utilizing nanofocused X-rays

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Product

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Conductivity and Local Structure of LaNiO₃ Thin Films

Conductivity and Local Structure of LaNiO₃ Thin Films