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Microscopic origin of symmetry lowering in NiO2 planes of NdNiO2 thin films

Identify the microscopic structural mechanism responsible for the non-ideal square-planar configuration in the NiO2 planes of capped NdNiO2 thin films observed by 4D-STEM dCOM, discriminating between Ni–O bond tilt/rotation, cation off-centering, or other distortions.

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Background

Four-dimensional STEM dCOM mapping reveals an altered NiO4 square-planar coordination with apparent oxygen doubling and a zig-zag pattern, indicating symmetry lowering in the NiO2 planes that could enable Dzyaloshinskii–Moriya interaction and spin canting.

The data do not uniquely determine whether the distortions arise from tilt/rotation of Ni–O bonds, cation off-centering, or another structural mechanism, leaving the precise origin of the symmetry lowering unresolved.

References

From the data, we cannot exactly identify the source of this non-ideal planar-configuration, which might originate from tilt/rotation of the NiO$_2$ bonds and/or to a cation off-centering.

— Signatures of canted antiferromagnetism in infinite-layer nickelates studied by x-ray magnetic dichroism (2403.16969 - Krieger et al., 25 Mar 2024) in Main text, paragraph discussing 4D-STEM dCOM results (Figure 4)