Limits to the strain engineering of layered square-planar nickelate thin films

Abstract

The layered square-planar nickelates, Nd _n+1 Ni _n O _{2 n+2} , are an appealing system to tune the electronic properties of square-planar nickelates via dimensionality; indeed, superconductivity was recently observed in Nd ₆Ni ₅O ₁₂ thin films. Here, we investigate the role of epitaxial strain in the competing requirements for the synthesis of the n = 3 Ruddlesden-Popper compound, Nd ₄Ni ₃O ₁₀, and subsequent reduction to the square-planar phase, Nd ₄Ni ₃O ₈. We synthesize our highest quality Nd ₄Ni ₃O ₁₀ films under compressive strain on LaAlO ₃ (001), while Nd ₄Ni ₃O ₁₀ on NdGaO ₃ (110) exhibits tensile strain-induced rock salt faults but retains bulk-like transport properties. A high density of extended defects forms in Nd ₄Ni ₃O ₁₀ on SrTiO ₃ (001). Films reduced on LaAlO ₃ become insulating and form compressive strain-induced c-axis canting defects, while Nd ₄Ni ₃O ₈ films on NdGaO ₃ are metallic. This work provides a pathway to the synthesis of Nd _n+1 Ni _n O _{2 n+2} thin films and sets limits on the ability to strain engineer these compounds via epitaxy.

Abstract

The discovery of superconductivity in the infinite-layer nickelates reignites an interest in the nickelates as cuprate analogues. Here, the authors investigate the role of epitaxial strain in the synthesis of the n=3 layered nickelate, Nd ₄Ni ₃O ₈.